I think it's fear more than anything, fear of the unknown. She may be depressed or have anxiety, it certainly sounds that way, with her saying that she's afraid of failure. It also sounds like her DH isn't a good dad; he's at home in the evening, so he should be involved in getting the DC to bed. Not because he's doing it as a favour to his DW, but because he's their dad.
If they do divorce, he's going to be in for a shock when the DC are staying with him during his contact time. But then, he'll probably hand over their care to his DM if she's able to, or he'll suddenly step up to the plate when he has a new girlfriend who he takes advantage of to look after them.
I don't think he's wrong to think that his DW should pull her weight in terms of contributing to the family finances; as I said, I know that my DH wanted me to find a job, and it was my intention too, until it turned out not to be possible. Not many adoptive mums are able to work FT, and certainly not when one of their DC has a lot of needs.
But he discussed it with me and made suggestions, he didn't just make snide remarks. He also pulls his weight as a dad to our DDs, which is essential with an adoptive parent; SS ask lots of questions about what their role will be.