OP, the only person you're responsible for is you. The best thing for you is to sever financial ties with any of your family members, because they're being unfair to you. This is what I believe you should do. It is totally legal to sever financial ties with your family. Their opinion doesn't come into it. It is your life and your money, you decide how to spend it.
This is what I recommend.
First. Sell the house you 50% co-own with your parents. It doesn't matter that they don't want to sell. You can force them to by taking them to court if necessary. Do it. If there is any equity, 50% of it is yours and 50% of it is your parents. This is your legal right, you'll have a solicitor involved with the house sale who will guide you through all your legal rights and responsibilities. Those are all that matters, not your parents or your brother's opinions.
Do everything legally. If another family member says they'll buy your share make sure it's done legally and in a timely manner, not by an informal arrangement. Trust nobody, none of your family will want you who is their cash-cow severing financial ties with them and they'll try all manner of nastiness to stop you doing so. Stick to selling, because it's what's right for you. If they hate you for it, so be it. Understand this - they already hate you, it won't make any difference, they're only being nice to you because you're paying for stuff. If they liked you and respected you, they wouldn't treat you this way in the first place. They can't claim to care about you whilst simultaneously putting you into a poverty state with their own actions by taking money from you.
Second. Let your parents sort out their own living arrangements for when the house is sold. Don't get involved with it, they have brains and can use them, they also have sons they can ask to help make phone calls etc if necessary.
Your parents have options:
They can apply to the council saying they're homeless and accept any help offered, if the council says they qualify for help.
They can contact Age UK and Citizens Advice Bureau for help with organising their finances, including help reducing debts, learning how to budget and claiming any benefits they're entitled to.
They can go live with your brothers or ask your brothers to pay for their housing and living expenses.
They can take their 50% of the equity and use it to buy a smaller home, if it's enough money.
They can take their 50% of the equity and use it to pay for a private rental.
They can return to work so they can afford their chosen lifestyle in a home of their chosen standard and size.
All these things are options for them to sort out their lives out. Which one they pick isn't your problem. If they don't like any of the options that isn't your problem either. If your brothers are unhappy about any of it, that's also not your problem.
Third. Arrange to evict whoever is living in the other property you own where their rental payment isn't even covering the mortgage (unless I'm getting confused and there isn't another property?). Use whatever legal means is necessary to evict them. Consult a specialist solicitor about this. Do not worry if this is also a family member living there. You can't afford your own life, so you certainly can't afford to be subsidizing someone else's.
This person will also have numerous options open to them for housing themselves and they can go to Citizens Advice Bureau to talk about it.
Once empty, decide whether you want to sell this property or live in it yourself. What is utterly ridiculous is your boyfriend paying your rent because you can't afford to when you own a house of your own. Either go live in it or sell it and buy something suitable for you to live in. If for some reason you prefer renting then sell it and use the money from the sale to pay your own rent.
You are currently using your boyfriend as a cash-cow and it's completely unnecessary. You have options that don't involve taking from him. You're only poor because you're allowing your family to take from you. I'd be angry with you if I was him. If you continue using him as a cash-cow you could destroy your relationship with him, just as your family have destroyed their relationship with you.