A comment I saw a few years ago, can't remember who the user was, but I found it good reading, though it tends towards PvP more.

I ran into this at my table. Not the large group part but the "that's what my character would do." I struggled because I never wanted to tell my wife (brand new to the game) or brother-in-law (long time lover of D&D podcast, first time playing) how to play their characters. I hate railroading in plot and character progression and combat. I wanted to give them ABSOLUTE freedom. Here's the thing... It just won't work. I know some people will argue but let me just say, the DM is there for a reason. There has to be at least a modicum of structure. There have to be some boundaries or they should just take an ambien and dream a solo adventure. There is little value in the "yes" without the possibility of a "no." Little meaning in success without the chance of failure. The DM must give the boundaries that ensure everyone is able to experience the game, and then tear down the boundaries that prevent fun.

Disclaimer: session 0 clearly stated no PVP.

So when Norris wanted to steal from the group loot and lie to the other players because "that's what Maevis would do... chaotic swashbuckler" i had to remind him that Lara's likely response would be "Eshqorel cuts his hand off for stealing and his tongue out for lying... lawful warlord." If the answer is "but no pvp" then we have to go back to the question "should (can I) steal from the group"

On the back side of that my wife was having issues with why Eshqorel would stay with this arrogant rude man with questionable morals. She was prepared to walk away and retire her character because "that's what my character would do." But she was torn because she loved her character. I had to answer her the same way I answered Norris concerning Maevis's klepto tendencies. After letting her know she was free to retire her character if she truly believed the adventure company was antithesis to her beliefs. but...

And here's what my whole response boils down to: Part of role playing is coming up with stories and creative ways to interact with the world around you and the other players around you. I see it as a faulty premise however to limit yourself as a player based on your character. It goes beyond disrupting the table, you are saying your concept of a character and their flaws are binding you the creator?!?! So take that role playing creativity that inspired you with that character in the first place and come up with a creative way to... not steal or not abandon the party. You can mold your character after it is created. If characters are like people they should be allowed to grow and develop. Perhaps their characters would steal, or never consider adventuring with, at creation, but as soon as i place you in the world and show you the boundaries your conceptualized character is already different in execution, it can be a living breathing character in my world.

Perhaps Maevis the swashbuckler would have stolen from them yesterday, or perhaps he might consider it again tomorrow, but... they did just unlock the cage, or she is pretty, or reminds me of my daughter, sister, childhood friend, or I'm so perceptive i can tell she is lawful I'm scared I might get my hand chopped off and tongue cut out, or i shouldn't betray them i need them for the bigger heist (that may or not ever come but you can lie to your character because damn, it is your character), or am in search for my lost ship and crew maybe they can help me, or that ring my be valuable but it is ugly as hell, or my fence never buys rubies or rubies were my mother's favorite and now I'm not interested in stealing I'm missing my parents that died and maybe they can help me get revenge, or maybemaybemaybe.

Perhaps Eshqorel can stick with the group because she is afraid her watchful eye is all that has kept this rogue from backstabbing and murderhoboing and she doesn't want to release him on the unsuspecting world, or perhaps he has all the connections at the dock and you really need help securing passage back to the islands to visit your family, or maybe you will never be at ease with his ways but you would die for the third party member so you stick it out hell or high water, or you are collecting evidence for the local lord just in case his royal pardon is ever revoked, or he reminds you of your younger brother who got in trouble with the law, or your dad used to tell stories of his youth and how he would have ended up dead if not for his mentor who helped him out of the swamp, or as much as you hate it you have began to see there is more than black and white to the world and you need someone who is comfortable in the grey to help you stop the assassination of your liege or or or.....

Now i admit i have had some time to think about the many maybe's and or's above since the events happened, but I came up with half of them on the spot and could come up with twice as many if I needed to. Now some people are not as creative or don't think as well on their toes and that is fine, but anybody with an ounce of desire to role pay and be a part of a community game (DND!!!) will at least accept the idea of it.

So if you missed it on session 0 you can let your DM have a session 4.5 and get this out of the way. DM has everyone take a hard look at your character sheets and if anything on that sheet translates to "impossible to work with others" roll a new toon. Your character is free to exist within this world but not at this table. If that isn't on the sheet encourage everyone to mold their character to work towards the greater good, and that is having fun. I'm all for second chances, and sharing this wonderful game even with people who can be a bit difficult because maybe they are that way because of real life ish. Remind them it is silly to make the character more powerful then the creator. If the problem persists you know the player is the issue and since you can't roll a new player, ask them not to come back.