What everyone else said ^^^^.
My suggestion is to figure out an exit plan. Sounds like you have a glimmer of one anyway - looking for part time work and so on. Make that explicit - figure out how to get from where you are now to where you want to be. I find having a plan comforting, even if the payoff is not immediate. I also understand that creating plans is so hard when dealing with mental health problems - it can seem insurmountable. So maybe start small. Plan how to deal with J's money assholery. Then how to get a job, save money, and so on.
Of course, if the only problem in living with them is that J is a bit of an ass about money, you may want to address that problem and if that is resolved (you got some great suggestions on that), you may enjoy living there. But it kinda sounds like they have some other issues that may impact you adversely.