From an outsider point of view, it seems to me that you are being taken advantage of in every way possible.

I'm so sorry you're going through so much. I can't help but think that a "come to Jesus" meeting might be in order for your son and your daughter-in-law. Have you talked to them about what is going on with you? About setting boundaries? Do they contribute financially to the home and other expenditures (like food, electricity)? I know times are tough for people, but I don't see why they need to live with you for four years...

I feel awful that you feel like a prisoner in your own home. I think it might do you good to write down what you're feeling, and maybe get up your nerve to discuss with them what you think should happen while they live with you. You are being very generous by letting so many people live with you, and to have them ignore you is rude. Do you think you would be able to have a talk with them about maybe not only what is going on with you, but talking about what is going on with them and what their plans are?