I don't think your MIL is likely to ever change. If your husband decides he is being unfairly taken advantage of, he might be able to set limits on her exploitation, but it sounds like he just goes along with her. That kind of leaves you without a leg to stand on, while you live in that home. I hate to sound discouraging, but the challenge you are up against sounds like a near impossible thing to turn around.

Maybe the birth of a son or daughter will make your husband focus less on his mom, but I kind of doubt it. If anything, this MIL is likely to try and take over the upbringing of this child.

It's good that you can earn your own money. However, it will be hard to hold onto it, while your husband's earnings get drained by his mother. That will leave you probably handling a lot of the expenses of your child, and yourself, and even of your husband. People who exploit others for money don't change. She won't change, and she has spent her life training her son to defer to her.

It must be hard, even heartbreaking, to have all this disappointment going on, while being newly married and awaiting your first child. Being a mother will make you a stronger person, but I dont know how you can change the dynamics in that house. It may take your husband fearing to lose you, before he will stand up to his mother. If you and he are good at communicating with each other, start talking with him, lovingly, but firmly. You will be trying to rescue him from his mother's brainwashing. She had a head start, so you have your work cut out for you. You probably won't get anywhere trying to confront the MIL directly, yourself. No one likes to feel fake, but you may need to keep up a pleasant face to her, while you quietly work on your husband behind closed doors. If your mother suspects you are trying to modify your husband's excessive generousity, she will probably try to undermine your husband's respect for you.

I hope you can keep your new, little family together. But keep that back up plan in mind, if you do find it becoming intolerable.