That's an intersting thought of choices for ME 3 squad member pathways, Celtic Latino. However, I felt strong ties to all of the characters the first time I played their mission and loyalty mission. Even though the romances were not as fully fleshed as some would like, I think they're going to take love interests up a notch - w/ ME 1 & 2 squad members.
If all of them survive:
Kaidan/Ashley - Whoever you choose to save may change the balance of the squad overall, but not literally. It would be interesting to involve characters in the same class and choose from Kaidan/new SM or Ashley/new SM for ME 3, not kill one or the other. If you choose one, then the other would command the Alliance base and raise their ranks. You could only pursue love interest if Kaidan or Ashley are on board. Plus, a new alliance SM should be on the way as well.
Garrus: I can see him redeem his status as a C-Sec officer, but not as a Spectre. He is still lost in his own selfish goals for redemption. However, if Sidonis or one of his "dead" squad members (like the Batarian tech expert) come into play, it is possible to choose one of the 2/3 as a new leader of C-Sec (a batarian might not be the best choice, but you can still use that incentive as to whether or not C-Sec would fully align themselves w/ a Batarian leader or not).
Tali and/or Legion - You can still pursue a love interest with Tali(if you chose to screw the council or let Tali go into exile), but she would go back to her people, despite her actions against her people while seeing Geth in their sights at the same time. This would be an interesting dilemma (and ties along w/ Legion).
Here would be possible outcomes for actions of ME 2 being carried over to ME 3:
1. -If you chose to have peaceful relations between Tali & Legion (paragon or not), then the Quarians and Geth would work together to see the real threat.
-If you did that converstaion successfully, but either Tali or Legion died in the final mission, then it might still be possible to accept peaceful relations (depending on the outcome of Tali's trial and you're decision to recreate or destroy the Heretics). Tali or Legion after the mission would be the sole voice of bringing both races together w/o conflict or bloodshed.
2. -If you have Tali & Legion, but you choose one over the other, then it is likely that Tali/Legion will betray you and retaliate against the Geth/Quarians, regardless of the loyalty mission. However, the Geth (+Legion) or Quarians(+Tali) will die if this happens.
-If you never have the Tali/Legion conversation, but you have one of the two SM's loyalty (and never got Tali/Legion until ME 3), then it is likely for Tali/Legion to betray you. To make this clear, either Tali alone defeats enough Geth w/o your help on Haestrom or Legion is taken by Cerberus or for you (but to NOT turn Legion on) and Legion will miraculously turn back on Normandy or Cerberus HQ by the Heretics/Reapers. Either outcome will lead to all of the Quarians/Geth dying in the process.
3. -If you don't have either of Tali's or Legion's loyalty, no matter how get them and whether both of them survive or not (in a worse-case scenario), then the Quarians and Geth will die. IF Tali & Legion are both still alive, then you can choose: kill Tali, kill Legion, or kill both of them.
Kal'Reegar may also be a possible choice if you choose to use him or Tali or Legion. If Tali/Legion dies, then Kal'Reegar will be possible. If both of them dies, then you would have no choice but to have Kal'Reegar.
Now...Wrex and/or Grunt: If both him and Grunt are alive by the end of ME 2, then you can choose either to lead Tuchanka (though Wrex would be the best choice). When ME 3 comes, there might another krogan (I'm hoping for the female Krogan that's into Shepard). If Wrex dies, then Grunt or the new Krogan must be lead Tuchanka. If Grunt dies, then you COULD choose between Wrex or the new Krogan. If both are dead, then the new Krogan will lead and you'll get a Varren instead (Urz or other).
Liara and/or Samara/Morinth: This would be a little tricky. (Battle sequences might be the same as Samara vs. Morinth) The ending result might have to been in this order, or it will not work.
- This part is only if Morinth was with you in ME 3... Morinth would likely would leave you to starting using ecstasy and hunger for her pleasure. But this time, she does so on Illium. Liara, now the leader of the Shadow Broker, realizes she has been killing people, and tries to resolve the problem w/ Shepard. Instead, Liara's troops die and ends up being a battle between Liara and Morinth. You can choose one person to kill. After choosing, instead of getting either SM (as sad as this would sound), you will not be able to get either squad member, but you will have changed their mind in using their abilities and powers to help you against the Reapers. By that point, if you go to Omega, Aria will be pleased and it will convince her enough to fight for your cause and have another Asari ready to take her place (whoever wouldn't matter - but I would say Seryna).
- This part is only if Samara is in your squad after ME 2, provided that you completed her loyalty mission...Samara either tells you or you find out on a dossier to find her on Omega. When you do, Aria would be "unjust" by secretly killing innocents in order to get rid of all the red sand (hopefully it's something better than what I just thought). Anyway, this charade ends up with a between Samara and Aria. You choose who to save. When you save Aria or Samara, she would not join you. Instead, either choice will give Samara/Aria the guts and confidence to take their place as the Matriarch of Omega (though it would be unclear if Samara would be abandon being a Justicar - it would be interesting if she did).
Jacob: Depends on suceeding in the loyalty mission (possibly better for it in ME 3) in order to choose for him to Alliance, Cerberus, or you kill him. In his place, maybe Kai Leng - the chinese infiltrator in ME: Retribution. But I do agree with you.
Miranda: Same here. But if she were to die; however, some new female character needs to take her place.
If Alliance and Cerberus SM's were going to fight against each other (since we know we can't have both or all three of them (Kaidan/Ashley, Miranda, Jacob, others)), then (if you have enough paragon or renegade) you can have each other make peaceful relations, choose for Alliance or Cerberus to leave the Normandy, or have them all shoot each other and for all of them die (2-4 SM's).
Jack: I agree with you on Jack as well. I do like the idea of going insane or suffer from decay or even turning to a mercenary organizaion. If so, it might be Eclipse. Then if has lived through ME 2, then you can choose between her or (I think) a salarian (female?).
Mordin: I'll agree with you again w/ Mordin. But if Mordin dies, who would replace him? (Mordin's son?)
Thane: If he survives on ME 2 (loyal or not), then it may be better to see that he is not permanently dead and have it take place on Khaje, the Hanar and Drell homeworld. They may have found a cure for him, but time would be scarce. It would be needed somewhere else, but heavily guarded. However, the boss may be Kolyat, who Thane wanted by his side before he dies. Kolyat is either forced under his will to take anyone down by an unknown enemy or he will not care for his father any longer and take you down. If you're a Paragon, you can convince him to give him the cure. At that moment, the unknown assassin will take the shot and you will see it at the corner of you're eye. When that happens, you can:
-Choose to sacrifice your life for Kolyat's and survive or
-Duck and have Kolyat get shot instead.
Regardless, the unknown assassin (probably Kai Leng from ME: Retribution) would have gotten away.
When you have the cure (if you completed Thane's loyalty mission), you inject it in Thane and survives. If Kolyat survives, then you can choose between Thane, Kolyat, or a new Drell (possibly female and the girlfriend of Kolyat). If Kolyat doesn't survive (but Thane was loyal to you), then Thane or the new Drell are options. If Thane is in ME 3, but failed the loyalty mission, it wouldn't be enough to save him and Thane would die. At that point, Kolyat wouldn't be an option, but the new Drell would be. If both Thane and Kolyat die, regardless of which bad point you take, then the new Drell will help you.
Zaeed and Kasumi: With both of them, they should actually be in ME 3 if you haven't already gotten them.
- If you succeeded Zaeed's loyalty mission, then he would take his helmet off and be able to help you, but only if you either resolve disputes between him and the unknown Blue Suns Mercenary (w/ the helmet from The Reprisal). If you failed to, then you have no choice but to kill him because you had betrayed him with the Renegade response. At that point, you might have the unknown BSM (or you could kill him).
- As for Kasumi, it'd be best just to have her and no replacement - regardless of having her as a squad member in ME 2.