Apologies if this is not the correct place for this question but I'm at a bit of a loss for what to do and would appreciate the advice of an experienced GM.
My party have been playing DnD 5e since July 2017, I DMed us through Lost Mine of Phandelver with a lot of success. At the start of the campaign the players all rolled their own characters and I asked them to write back stories as I was writing homebrew story hooks based on these for the future. We started out with 3 players but by the end of the campaign we had 6. The character who was added around session 3 was met with distrust from one of the original characters (we'll call him P1) and this escalated quite a lot due to drunkenness on the P1 player's part. In a later session this was revealed by the player to be a racist dislike for all dragonborns justified by an event in P1's backstory. I was unsure of this but the new player was happy enough to roleplay it out but over the course of the rest of the campaign, this was never resolved - an explanation has never been given in character though all players know why the character behaves this way. P1's character still says horrible things to the dragonborn and makes a point of stating how much he dislikes him at any given opportunity.
We finished LMoP and started onto my homebrew stuff. P1 and another player were often not able to attend DnD due to other commitments and we decided to pause that campaign until we were more available. One of the other players has DMed through some homebrew and the start of Tomb of Annihilation for about 3 months - P1 behaved a little better during this, no racism, just a bunch of spotlight stealing.
We've recently resumed our original campaign and P1 player claimed that he had lost his character sheet. Fine, I say, choose to roll a new character or remake him as best you can based on memory. He elects to remake this P1 character - the only thing is, he doesn't remake the character at all the same. Half way through the session, the character is revealed to be multiclassed now sharing the same class as the character he is racist against. Another cause of tension. In fairness, I should not have allowed this - I should have put my foot down then and there. But we were mid-game and I didn't want to disrupt it for the other players. I should have fixed this after the session but I was hoping it wouldn't be a problem. He had also forgotten his whole back story which is very frustrating for me as I put a lot of work into the plots surrounding it.
In our most recent session the P1 player was more disruptive than usual - changing things about his character [including giving him an obnoxious accent], interrupting me, talking to me the person not me the DM or NPC about things irrelevant to DnD in the middle of the session during other characters conversations with an NPC and trying to talk to other NPCs while I'm speaking with another character. Claiming to have magical abilities beyond what was previously agreed - a cantrip being used like it's some all powerful spell and then long arguments that I said he could do it last week, etc. The other players were frustrated and a few of them mentioned it to me after the session. Our dragonborn's player has also stated that he now dreads sessions when he knows P1 player's character will be present.
It had come to a head for me. We'd jumped into all this without a session 0 so I decided that I needed to make my expectations clear. In an effort to iron out the misunderstandings between us all I scheduled a Session 0 for this evening. I sent a list of questions with the options of sending answers to me to be discussed at the table or just answering on the night. P1 player obviously elected the latter. But lo and behold, we get a message this morning that he is 'sick' and not going to attend tonight. I have suggested that we Skype him in and he is ignoring us. Most of the other players think he is avoiding the session because he doesn't want to have his behaviour brought into question.
How do I proceed? What is the best thing to do here? Do I just send him the answers to the questions decided by the rest of the group? Do I demand he sends his answers?