I don't know what to say. It's a horrible situation, everything is. Huge resentment on your behalf with you life, kids, husband and mum. Mentioned numerous times before, therapy would help you out so very much.

If you want to get peace with your mum, then go. You do not need your husband there, you really do not. You talked before about wanting to be stronger, then let this be your big first step.
And no, there is nothing wrong with wanting peace, it's time to do things for you, and not worry about anyone else - that includes doing less for you husband and his children if it helps you let go with some of the resentment and be a little happier. This is what I mean by actions - it's lovely that you do all these things for your husband/his children, but without his support to put things right (and his role as the father) then you need to start putting your foot down and insist he does it or refuse to have them until he does. And stop doing things like the clothes - buy new ones to wear while they are with you, and send them back to mum in the old ones. Stop playing into the mum's hands and hopefully it will stop - if not, at least it will stop being so upsetting to you because you're not giving her the satisfaction. Oh, and I would keep a note of all the abuse she has left for you and harassment in a book - you may need it one day.

The thing is, we can get upset so very much about other people's actions, but it's important to know that if reason, caring or kindness does not change the way they keep walking over you, then there is only you and your own actions left. Getting more confident, getting fairer about the way you are treated - if demanding doesn't work, then withdraw some of the kindness you keep showing. Be tougher. OK, it sounds tit-for-tat, but without you putting the effort and emotional effort in, you'll start to feel less resentment and things will wash over you a bit more because you're less emotionally invested. And who knows, it may make other people finally see where you are coming from and improve their behaviour towards you. If things do not improve at all at home, and you are never happy, then perhaps there will be a time for a rethink.

We really can only do our best to make sure our own happiness is there. It's unhealthy and wrong to keep putting other people's happiness before our own, esp if it creates resentment.