I have done 3+ runs and never received them. Getting Vivienne's is easy through dialogue, but I didn't even know Cassandra and Leliana had war table missions.
I completed 3 runs:
All my toons are female so romance is irrelevant for Cassandra, I assume. I would hate to think that my fling with Iron Bull had any bearing on who sits on the sunburst throne…
First run- I wanted Cassandra
1.) Got hardened Leliana
2.) let her murder people
3.) supported chantry reform
4.) sided with mages (allies) and kept wardens as allies
5.) Supported Celene only (no elves)
6.) Never received war table mission for anyone except Vivienne (didn't do it)
7.) I encouraged Cassandra to become divine
8.) I told her to reform seekers
9.) Discouraged Leliana from becoming Divine
10.) B**** did it anyway. ARGH.
2ND Run- wanted Vivienne
1.) Got Vivienne
2.) Agreed with her about Circle's necessity (Vivienne was my BFF)
3.) I supported circles & chantry reform
4.) Sided with mages (conscripted) and kept wardens as allies
5.) Supported Celene & Briala ( twisted love conquers… Orlais!)
6.) Never received war table mission for anyone except Vivenne (I did it)
7.) I avoided talking to Cassandra and doing all her personal quests
8.) I told her to reform seekers
9.) I avoided talking to Leliana and doing all her personal quests
3RD Run- wanted Leliana
1.) Got Cassandra
2.) Put the chantry down
3.) I supported mage freedom at every opportunity. I was annoying with it.
4.) Sided with mages (allies), told wardens to get the hell out of Dodge.
5.) Tried to get Gaspard, Celene, and Briala to work together, I don't think it worked out for Briala though…
6.) Never received war table mission for anyone- I avoided Vivienne
7.) I did some of Cassandra's quests- the Lord Seeker one. Not the others.
8.) I told her to reform seekers/make them better. Discouraged her from becoming Divine.
9.) I did Leliana's quests (she was softened). Supported her to become divine.
10.) And it went to CASSANDRA.
Conclusion: This is silly. I think there's a bug for it to be so unreliable with who becomes Divine.
Also, reading other people's choices and outcomes, I have had drastically different choice combinations and some are even exactly the same- I ALWAYS end up with the opposite candidate of whom I should logically get. If I support Leliana I will get Cassandra and if I support Cassandra I get Leliana. Vivienne is the only one that I seem to have a modicum of control over and I'm pretty sure it's the war table quest that locked her in for me. I think there might actually be a bug, which would be unsurprising. It really shouldn't be this complicated. The game is too long and I have a life. It's annoying that some off handed remark to stupid Dorian might alter the course of WORLD EVENTS. Or maybe it's because I killed Ruck in the deep roads. I'll never know.
UPDATE: I completed my 4th run and got softened Leliana- which was my goal. The differences were that I stopped saying 'I don't know' about anything religion and said things like 'i don't believe in your gods' etc. I NEVER wavered on it. I also told Cassanda to 'forget the chantry' instead of rebuild the seekers. Though she ended up doing that anyway. I also reconciled Briala and Celene.
What I don't like about this system is that it feels like Bioware is imposing a 'type' onto our characters. For example, if I want Vivienne, I feel like I have to 'say certain things' or make 'certain choices' that might go counter to what I initially wanted for my toon's personality. It forces my inquisitor to conform to a certain type just to get the Divine I want. I suppose it's easiest if you just don't care either way. 