Can't tag a PP but there was a comment about how OP shouldn't have to work to the bone to provide nor not be able to parent the way she wants (presumably referring to her wish to go part time) because of this.
For me, there is no suggestion OP is having to work to the bone. It just sounds like she is working full time in a job she would prefer not to do. It also isn't clear if her husband wouldve been happy with her working part time - I'm not saying husbands get to dictate but I am anti the presumption that it's a mother's right to be the one who goes part time, or for any parent to go part time, just because they choose - it should be a joint agreement. So any resentment based on not being able to do this is only relevant really if absent the payments OP and her husband wouldve both been content for her to be part time.
What is a huge issue for me though is the lack of any consultation from OPs husband about paying for his parents. This really is something that in my view should be discussed and agreed as it comes out of the family pot. In this case, it isnt just husband's contribution to the pot being reduced as a result but actually OP is having to contribute in effect as they do not have enough money otherwise. I would still have an issue with the lack of discussion regardless of income but if OPs husband was a high earner and could make contributions without it really impacting the family, it would plainly make a difference. His immediate family should come first and then if it is affordable his parents should come next if agreed between him and OP. If not agreed, he can choose to go elsewhere and contribute by himself but of course would also need to then contribute to OP.
Personally, I have wonderful parents who have supported me hugely. Therefore I couldn't see them destitute without helping them however I could. I know my husband agrees because we have discussed it even though it isnt yet a likelihood. They've done a lot for him too. Any contribution would, though, have to be affordable and I wouldnt be paying for them to live a lifestyle above our own like some people seem to be doing. I have a child and need to also think about her and her future, as well as retirement planning for myself so that she doesnt have to worry about me. So it is a balance and for me depends on what parents really need and also what is affordable. There is also another relevant consideration for me - the relationship with those parents. If my parents had treated me like crap growing up, squandered their money and made no effort to sort themselves out when they could I would be much much less inclined to help them. But they have helped us with childcare saving us so much money, helped us with IVF and are also huge emotional supports. They more than deserve to be helped in old age and if they dont need the money, I would still do what I could to help with their care even if they needed to live with us to prevent them going into a care home too soon.