Remember my comparing a WAS going through a MLC with a toddler going through the terrible twos and a teen going through puberty? This comes to mind now. He is really throwing a fit to get what he wants at all costs, isn't he? My goodness....
My thoughts on this...you cannot control what he says to your children. All you can do is be there for them throughout this conversation and importantly after he leaves. Take no ownership in the decisions he is making, but do not speak of him in a negative way. Simply tell them you love them, will always be there for them and are doing your very best to make the best decisions for them. He is making lots of threats right now in an effort to get the kind of car he wants (good grief!), but hopefully he will think with a cooler head soon. With regard to selling the house...are both of your names on the mortgage? If so, he can't put it on the market without your signature on it. So again, do not let him scare you into making decisions you do not believe are best for you. Seek the advice of your attorney.
It seems that he really believes he is in total control of what happens. That is wishful thinking on his part. The matters he is bringing up should be made by the two of you together or by the court if you cannot agree. He is in for a very rude awakening that absolutely everything he wants isn't going to happen.
I am really, really sorry he is doing this to you and the kids. Big hugs of support to you...hang in there.