Rather than start a new post on this subject, I think it makes more sense to add my thoughts here.
I completely agree that members of a party need to be handled as a likeminded entity whenever they're making an effort to perform an activity together. I am not talking about scenarios where two players are intentionally playing apart within the same game, but rather moments where everyone is present at an event and contributing towards its progression. As an example, matters like reputation adjustments with companions and/or NPCs should occur party-wide to all present, especially when there's a consensus between players on the dialogue options being used.
This particular issue with how multiplayer is handled in parties existed as far back as Divinity - Original Sin. The difference is that this flaw was thankfully corrected in a patch after feedback was given, such as this thread below.
Guilt & praise by association, attitude score woesOn matters of reputation adjustments, I provided the following argument then, and I feel it still makes sense today.
I'm still running into examples where both characters are present at an event, but only one of them receives an attitude adjustment score.
For example, if you have your two adventurers (Tom and Sue) file a report about the lost sheep to its owner, Bertia, the only one who Bertia ends up liking is the one who had the conversation with her. In this case, if Tom is the one that informs Bertia that her lost sheep has been found dead at the hands of the mortician, then Tom receives a massive attitude bonus with Bertia, while Sue (who is standing right there thinking "I helped too!") receives nothing.
I feel that if both party members are present at the time when an attitude adjustment is made, then the adjustment should apply to both of them (particularly in the case of positive adjustments). In the case above I feel like one character should be smart enough to say "Bertia, both Sue and I found the corpse of your sheep during our investigation. Together, we confronted the mortician and got a confession out of him. We came here to tell you the news right away.".
Now, I realize the developers want it to be possible to create a situation where one character is loved by the town and the other is hated. And that is why I'm specifically speaking about events that happen when both characters are together. When they're adventuring apart or speaking to NPCs while separated, then treat them as individuals. Otherwise, it should be a team effort. A team effort should equal team rewards or team consequences.
In addition, what others are saying in this thread regarding having access to the entire team as a resource also makes sense. If Tom is having a conversation with an NPC and Sue is listening in, and an insight check needs to be made, then both players should be able to perform one. And (in this example) if Sue succeeds and Tom fails, then Tom should be able to benefit from Sue's success because this is a group effort where there is a mutual interest in succeeding. And, if you want to provide Sue with the option to withhold information from her team, then that's also great - but obviously it's extra work to implement. But there should be an option for teams to share resources like this somewhere.
I'm concerned that this is still a problem years later, as this is one of those issues that needs to be fixed by launch or it will negatively impact playthroughs starting then, particularly in areas of reputation.