My premise is, that the group is essential to the fun and usually everybody knows that. So it is expected of the GM to help the group overcome problems caused by correct role play of the characters and unite. Incorrect role play should not be allowed, much less when leading to splits.
My General idea
My concept isn't rocket science, but It may help to formalise it nonetheless.
- nobody should be punished for an action that is in character. It
should be allowed and dealt with in game. Voicing preferences out
game is immersion breaking
- Follow the process of allying and bonding in real life. We may bond for a short time, due to necessity. The DM has plenty of ways to force that. Having braved some dangers together greatly increases the likelihood of bonding.
- An even stronger motivation is an overwhelming foe.
- As a DM assess the compatibility of your crew beforehand. Some flavours of hero tend to be very problematic. Particularly those skilled in mind control or able to haunt people's dreams!
I mostly play TDE (where orcs are playable), but in this context it doesn't matter. My favourite GM usually allows splitting to happen and adapts to it, making it very appealing for the characters to unite. Here's an example:
As a white magician who needed money, I was keen to make myself useful to the local guild. There was indeed a quest centred around retrieving artefacts from a remote tower, where dangerous things were going on. I had good reason to think the task a difficult one and needed a party.
But when I spoke to the other players in an inn, the thief was (wrongly) worried I might recognise her as a convict, because I had spent time in a city where she was (later) wanted. Totally in line with her character, she incited the orcen fighter (whom she had charmed) into beating me.
So we split up and the DM played out the thief's side of the party first. Pretty soon, she went for some pickpocketing, or cheating at cards and was caught. The others were five fighters and our fighter never had a chance. When he woke up they had shaved him, stolen his treasured weapon and the girl was gone.
Unsurprisingly, these were the bandits from said tower and they had abducted the girl. So, the orc first needed to find that out, but then he had every reason to join me.
On the first night, the DM had two games to manage, but little happened on the girl's side - hidden from us. Perhaps that was his way of reminding her she should have voiced her concerns about my magician earlier. Of course, a lot of cooperation was needed to rescue the girl from the bandits, who had been under a dark cultist. After that:
- the orc and my magician had bonded in a funny way. Even more so as I helped regrow his fur.
- I was obliged to go after the whole organisation, because there were dark cultists involved.
- The girl was compelled to do it for revenge and because they had implanted a kind of hocrux into her.
- The orc was loyal to both and helped their alliance.
Note that, when splits occur, seasoned players can sometimes have very useful in character chats in a nearby room. Of course nothing "technically" relevant can happen without the DM, but a lot of chat and role play.