He can say what he will about you. You need to make sure they respect you. They will love you but wont understand what he is saying.
You cant stop what he says to them - but what you can do is make sure they respect you when they are with you. Dont let them speak/treat you badly, no matter what his mum is saying to them. They know but will be confused.
Have you got a lawyer and any close friends/famly that can help you? Also have you been in touch with Womens Aid? They dont just deal with physical abuse - they can help you too.
I am in Scotland but many lawyers here will give you 30 mins advice free with the idea that you use them in the future.
How about going to Citizens Advice too?
There are lots of places to get help.
You are not alone in being in this position but you are not helpless-there are places and things you can do.
If I can help you more - please let me know.
You too can tell your kids how it is. That it is not right to live your life by putting others down. That that is the behaviour of weak men not strong ones.
He can be taught that this is not the way to trat women, nor you.
You can do this WW - you came on here, and we can help - there are lots of us who have been here too.
Be strong - you are strong and you are their mum - that is so important and so are you
I went through mediation a year or so ago, also with a master manipulator and was soo scared I cried all the way from reception to the meeting room and my ex was with me maintaining a frosty silence! Not the best start! My ex was also refusing to leave the house at the time.
The mediator was fantastic and was very fair in making sure that we both got to speak and managed to calm my ex down or point out when either of us was being unrealistic.
In hindsight, I wish that I had not agreed to anything without being strong enough to say, 'OK, can I have a week to think about that proposal' rather than agreeing to some things just to move the session along.
My tips to you would be to make the session as early in the morning as possible and try not to see your ex for as long as possible after. Just before you go in, remind yourself that in 1 hour you will be out again, so take a deep breath and stand tall.
Don't forget the mediator is there for both of you and they will ensure that you get to say your piece. If neccessary, let your ex say what he wants first and wear himself out, the mediator will make sure that you get to say what you want as well and will make sure that you are not misconstrued.
The mediator will review everything that is said so if you have changed your mind about anything, you can say so.