Regarding Anora, to spare or execute Loghain never comes up in the dialogue with her before the Landsmeet. To avoid being betrayed by her probably requires selecting specific dialogue options at the beginning of the Landsmeet. You should probably check with the Dragon Age Wikia to get that dialogue correct. I also can't help but wonder whether your level of cunning also impacts who sides with you and whether Anora stays loyal.
It does get addressed, though only if the player picks that option. It's one of the many permutations of the landsmeet. In the dialogue with her at Eamon's estate before you go to the alienage, whether you arrange the marriage to your Male Cousland or Alistair or tell her you will support her, if you don't specifically tell her, (paraphrased) "your father must pay for his crimes", she will continue to support you when the landsmeet comes. If you choose the dialogue option that tells her he will be paying (which usually means death) for his crimes, she will turn on you at the landsmeet. You won't know this till the time she steps in however, as she plays her cards close to her chest, revealing nothing at the moment you speak to her at Eamon's estate.
Anora has her limits, and being party to knowingly killing her father is it. Nor will she marry the man who killed him. If Alistair does, she refuses to marry him, even if doing so costs her the throne. If the PC does, she refuses to marry the male Cousland. She forgives the PC for Loghain's death, she's very pragmatic like her dad and has a lot more worries on her mind than personal revenge scenarios. But she still refuses to be intimate with the man who killed her father.
As for OP, no you can't have Alistair in the party with Loghain. Loghain is his 'crisis point'. The most you can do is harden him, marry him to Anora, and recruit Loghain. Even then, Alistair leaves the party to do king-stuff, and you get Loghain. If I recall, I don't think he's built that well to be a tank (stat wise I seem to recall a crapton of willpower instead of strength or con), but if you're playing on casual mode, he will do adequately (my recruiting warden was a rogue and I replaced Alistair with him). if you are playing more difficult modes, you may have to drop it for some fights, or use mods to boost him (if possible) in stats you need to make him more effective.
He does come with "Champion" spec and a somewhat decent set of massive armor if I recall correctly, which helps.