It sounds like you are doing an amazingly good job given everything that is going on, well done.
It also sounds like you need some support, which it doesn't sound like your family or ExHusband's family seem able to give in away that is helpful to you.
I would suggest that you look at what it is you need to feel better, counselling, some time on your own, and then plan to get it.
Your GP can refer you for counselling, but if you are a student, I think you are, you better bet might be your college or uni as they often have counselling services with much shorter waiting lists.
Could you ask tell your EXH's mum and/or your mum/dad that they can have DS for a morning or evening a week every week to give you time to breathe/have a bath/cry/go out with a firend/whatever? If they can't do what you want just say fine, but that is what is on offer...
Could you tell your mum/dad that their comments are unhelpful and you would be grateful if they would stop saying them, how do you think they would hear that? Would they be able to?
Finally if you are worried about money contact the CAB and see adebt advice worker who will help you draw up a budget, make sure you are receiving a full entitlement of benefits and negotiate with any crediotrs.
Your HV is a screaming cow, don't see her again. As everyone has said what she said is just rubbish, you sound like an effective mum who is doing the very best she can in very difficult circumstances.
very big, very un-mumsnet hugs!