They are living in your house, but keeping their son away from you, and apparently both your son and daughter-in-law are treating you like dirt under their feet!
What have you to lose by asking them to find accommodation elsewhere?
You are already estranged from them,
You are made so uncomfortable that you stay in you own room, instead of going where you want in what is, after all, your house.
If they move out, you will be able to go where you want and do what you want in your own house.
If they are not paying rent and their share of utilities' bills, home insurance etc. then you will be better of f without them.
Frankly, if money is an issue, you would be better off renting a room or two to a total stranger, who could be expected to treat you with respect.
I admit, I do not remember all the details of your previous situation with them, but honestly, it cannot get worse.
In your place, I would give them two or three months' notice and refuse to extend it, irrespective of how hard it may be for them to find other accommodation.
Has your DIL no family, they could live with for a change, if they either cannot find a house, or cannot afford one?