Well , I think this should work like this : If player wants everyone in party to engage then they should start conversation while all members are linked. If they want to sneak and kill/steal or do other stuff while party is in conversation, they should unlink respective members and they will not be able to join in. This will provide more agency to player whilst keeping broad range of conversation options too.
+1 again. Totally agree. In fact, I'm about to post another suggestion about Group Stealth. I was thinking about it, and I don't think Group Stealth is really the answer. Solasta has a Party Toggle Button. You hit that button, the whole party moves together. This is a good button. BG1 and 2 and many of the old games had something similar. If I hit the button and start moving, everyone forms up and rejoins the party. If I hit stealth, everyone stealths. If I unstealth while in party mode, everyone unstealths. If I jump in party mode, everyone jumps.
So similar to how they have Group and Ungroup right now, but make it a button, not a Right Click on each individual person thing. If I click on the Party Mode Button, everyone forms up. If I click on an individual character, they are no longer Grouped and I can do whatever I want with that person all by themselves. Then give me the ability to hold Shift or something and select each party member I want to chain together in my group as well, so that if I want to exclude one person I can do so easily without right clicking and ungrouping them. They could even still leave that functionality in the game so if I have everyone grouped and I want to ungroup someone, just that person, I have the option of right clicking and ungrouping. But for most situations, I should be able to just click on their portrait and they ungroup.
Then, if I want a certain person to be the Group leader, I click and drag their portrait to the left-most position. Boom. Team Leader when Party Mode is selected.