I think my C6 will do the same, even if he has no job, he will still give the same amt of 家用 to 99.
My 62 just died and 99 inherited $. I told C6 that you can just not pay your mum la as she has lots of $. My C6 said of course cannot lah because inheritance is a different thing. It's his responsibility to pay parents' living.
Yes, your husband is a good son and he has obligation not just to you but his mom, too. I think unless his mom says no to the monthly allowance, otherwise, there is not much you can do.