It's common for people to struggle with the transition to adulthood.
When we're kids our parents are supposed to look out for us, and tbh, if they don't, there's not much we can do about it except rely on other people's goodwill.
Then we're adults and it takes time for some of us to realize that WE are responsible for our own well being, and that of our kids. WE are now the grownups. The rules have changed, and are now #1 look after ourselves (put on your own oxygen mask first) #2 look after the kids.
And we can say NO in our own house.
Did you never see your parents sticking up for you or for themselves?
Role models are so important, if we don't get to see people doing various bits of adulting it takes a lot longer to work it all out.
I'm kind of saying, from this point on, your priority is to sort your own needs and wants and those of DS, and only once all that is ticked off do other people get a claim on you and your resources. You get to weigh whether doing x or y is in your interests, and you get to decide not to do it if you like.
In short - drop most of the stuff where people don't reciprocate and firmly turf them out if they're being pains in your house. But if you never saw that being modelled I get why you don't do it automatically now. You can though! It can be scary at first but is absolutely doable. Pretend you are confident even if you don't feel it inside. Don't give up If there are hiccups. Once you've stood up for yourself successfully things feel so much better and you feel in control of your life, so it is so worth keeping at it!