Ultima 7: Yes, with a few brief plot-related exceptions in The Serpent Isle.
To be honest both games (more so with Ultima 7) party members just does not feel right, Its like in a way this game was originally meant to be a solo character, but with party members tacked on. Did you felt the same playing both games, because they sure are not Baldur's Gate party system thats for sure.
What the title says because after playing around with them the party member system just feels like a hassle and I rather just go on my own.
I know with Ultima VI you MUST have one party member for a bit to get one of the runes. Not sure on VII though.
So is there also a way to ask a party member to leave in Ultima 6? How do you do that (and excluding just getting them killed and leave them for dead)