So is there no way we can have an effect on each others conversations? Like in Original sin where your partner can chime in and either disagree with you and chance it.
There are places where this can happen, limited to bigger choices. They'll chime in, in the middle of the conversation. Also if you have other Origin teammates, they will chime in as well. For example I was going one way... and the non-main Origin chars both chimed in automatically and said "I wouldn't do that". Changed my mind, other coop-player theirs and we moved on.
In general it does take some time to understand the system in place here.
To get/advance MOST quest options only one has to talk to the NPC.
But, your teammate may have a personal quest tied to that NPC, so there is that. If you both don't at least chat a little you may miss it.
Also one players character maybe able to advance a quest differently.
It is complex and that makes it a little confusing/cumbersome. But if you do both players, you may pull out a nugget.
I do like it overall and it is super nice if you can choose your choices carefully, you can get additional dialog and a reward given to you for saying the right things to that NPC. That reward alone makes all players want to talk to each NPC, just to see.
To me, they are blazing new ground here. Not perfect, but better than nearly anything else.