He doesn't care about your feelings. I once asked DH, why is your default to criticise me or make negative comments about me. This was mainly done when with the extended family.
Its like he felt the need to say something if one of them was having a moan or saying a pet hate about their OH.
I don't think he realised it... he stopped doing it after that.
If you're still having MC raise the issue there.
A joke is only a joke when everyone finds it funny.
His behaviour is similar to bullying by isolation.
A few suggestions...
Do some activities with just you and the kids. Talk to them generally about kindness to others...not hurting feelings or making hurtful jokes about others at school. Generally about being a nice friend.
I was bullied at a point in school, so as early as possible I spoke to my DC about kindness and never being nasty to people, even if they didn't like them.
Invest in time for yourself to do your own thing. It could include time at the gym, regular beauty treatments, a new hobby or interest.
Do things that make you feel good and ignore him.