Assalamualaikum,
I've just sort of caught up.
Fruitcake, a step parent is not compelled Islamically to care for their step child financially.
That is the responsiblity of the biological father, any money a step parent spends on their step child is a huge act of charity, any money a mother spends on her children is the same as it happens, a charitable act not compulsory.
Having said that a step mother is not compelled to care for step children, the biological father needs to sort out care and residence for his child(ren), step mothers are not compelled to become unpaid childminders for their step children.
Custody of a child islamically goes to the father on marriage of a mother, however, custody means the child sleeps at the fathers house, also the child if old enough gets a say in whom they reside with if both parents are equally suitable as main carers.
If the mother is having affairs and kicking her child out of the house, she is clearly not the best person.
The children caught up in this maelstrom are the ones who have suffered massively in this.
I think sis you really need family therapy, or at least therapy yourself to heal from your own trauma and start seeing things in perspective.
I'm sorry ot say, your husband sounds weak and useless and honestly and personally, I would not will my house to him. That would go to my children only. I am not speaking idly here, I'm divorced and my beneficiaries are my children, a husband if one comes along will manage just fine as he no doubt is doing currently whilst not married to me!
Either go to your GP and ask for help you do sound depressed to me, but then who wouldn't be with having coped with so much? Or look up Islamic counselling, some masjids offer marital counselling, I think your marriage would benefit from it.