Hopefully the girls will have a little more understanding of mh issues then exw and appreciate that yes it was shit for a little bit but he worked hard to overcome it.
I am tue girls, as in: one of two sisters that grew up with a mentally ill father who wasn't contributing a penny.
IME, yes, we understand MH issues. When we grow up with a parent who has them, we understand the fall-out better than most. But don't think it doesn't grate. It's not an intellectual thing - it's a childhood spent with your emotional needs (on top of your material ones) going unmet by one of your parents.
It's the small things that really hurt: your towels, for example.
Every grown up child will understand genuine inability to pay maintenance. No normal adult will look back and understand their mother being berated and vilified as the exW is here.
Growing up with a mentally ill parent is kind of crap to start with, actually. You don't really get the emotional support you need from at least one parent. And then you grow up and grow to realise, on a purely intellectual level, that this may not have been malice but genuine inability. But that doesn't undo the hurt and the feeling of abandonment. It doesn't magically fix your relationship with your parent.
Working hard to improve things is obviously the way to go. But until your husband can actually give those kids everything they need it's twice as important that they get everything that they possibly can. And I mean this for emotional much more than financial reasons.
Slagging off the mum is just very much not that.
On behalf of my own, lovely, brave and very often desperate mother who raised two little girls alone, tried to make sure we actually had some semblance of a relationship with our father, paid for everything we needed and - yes! - took us on foreign holidays, I find this very unfair.
Your DH needs to get help, obviously. And you really, really need to stop blaming the ex. I get that you may not be able to contribute much financially - and if that's the situation it obviously needs to be fixed ASAP and will be understood later if it is. But making it out as though the kids' needs are an unacceptable extravagance is inexcusable.