Can't stand all of these things, to be honest. It should still be possible to take them with you together and exactly because of their rivalery/whatever there should be interesting situations because of it.
For me, it's just arbitary and the game saying "No, you can't do that. Here's exchangeable story reason #234343442.*
If anyone of you have played Jagged Alliance 2 1.13, you may know that it had similiar character relationships. Some people hated each other and other loved, etc. Great thing in that game was that it was up to player to choose if he wanted to have these relationships affect gameplay. If you didnt like it you could turn it off from ini.file. Thats where you changed settings in that game, if you dont know it...
I hope that this game will also have wide range of settings for player to choose the ones, that they like.
Btw, if you like turn based tactics JA2 is the game you should play.