Kurt, I'm so sorry it's turned out like this.
You sound much brighter and stronger, and your family are fantastic.
I agree with the wise words posted above- get anything of value (financial and sentimental, e.g. photos) which is yours or jointly owned out of the house and to your parents for safekeeping. You don't yet know whether you'll be staying there, and clearly he is away most of the time, so you are keeping the marital assets safe rather than leaving everything in an empty house.
Same applies to documents -you need to keep safe any paperwork which is yours, the children's , or relates to any joint ventures or bank accounts, plus proof of household income.
If you can get there before he arrives- going with your dad or brother is a great idea , if your mum can look after the children- then there is no room for him to argue about what's what. And then letting him arrive back to empty house, with all home comforts gone, might help him to realise that you are moving on without him, and he is now the one being left behind.
It sounds as though he has detached so much that he could try to avoid paying what he should be- it'd be worth getting professional advice before agreeing to anything he suggests. He's likely to try to withhold money so that he can maintain his single lifestyle, rather than prioritising feeding your babies. Remember that having the support of your family does not mean that your partner escapes his responsibilities to his children.
Hope you have a lovely day with the children. One day, when all the young workmates have moved on and settled down, and your partner is alone in a bedsit somewhere, he'll look back at what he's thrown away.