This doesn't fit with my remembrances of BG1/2, where it was totally possible to have a party with say Edwin and Minsc together, or Jaheira partied up with the Zhents. Just going by the first people we met, the initial party comp in BG1 would have been Charname & Imoen, Monty & Xzar, Jaheira & Khalid, so basically covering all the bases for a mixed alignment party.
In BG 1-2 it was working only to some extent with companions of opposite alignments, only if to keep it all neutral, or they would leave. But some companions were not able to be in the same party for long. Edwin and Minsc would not just leave party, they would kill each other, both in BG1 and BG2, and I think there was no way to talk them out of this. Same if to keep Jaheira & Khalid and Monty & Xzar in the same party for some time they would also start fighting. Though Jaheira is true neutral, so it was possible to keep her in evil party, especially without Khalid in BG2. Perhaps it was possible to cheat the game somehow and to keep them together, but it wasn't devs' intention, in general it was not a good idea to keep such companions together in the long run, you don't want them to kill each other in the middle of some dungeon. In BG3 we have very little of this and it's always possible to talk them out.
