He's your brother, I think you know or could know if you deeply think about it how to keep him alive and hopefully start a new life. If you play out the scenario he's in now in your mind, how will you and your family deal with the loss. I would gather the family together, express your concerns and ideas and come up with a plan together. In the exteme, if everyone in your family rights him off, then it's your decision to go it alone. They simply might not be in the same headspace you are at the moment, can't deal with the reality, don't have the tools, skills, emotional strength or imagination to help him now. Sounds like you need professional help either privately or via public services to either advise or help execute a plan to get him the help he needs for long term success. He needs a way to have or find food, shelter, medical care, and a reason to exist every day for the rest of his life, likely independent from his family. Ok, that's doable, just try whatever you think will work.
What do you want for him, what does your family want, what does he want, what do professionals want? Come up with a plan and just try it.
Would you like to see him in a drug rehab program, 12-step program, religious program? Maybe eventually living in a group home setting with other people who are recovering? Working a job or volunteering within one of those programs or settings? Just think up ideas, share them with everyone involved, think about short and long term goals, and not just short term fixes that won't be sustainable.
In the immediate situation, figure out how to see that he's warm, fed, can take a shower, and have an incentive not to be actively doing drugs, or have some type of replacement for whatever they do for him to implement. Obviously you and your sister can't be alone with him, so with a family member or friend or maybe someone he used to respect who could control him, get with him and feed him and get him a shower if needed (even if it's a truck stop shower or something) then sit him down and tell him what you're thinking, assuming he's not completely strung out on the dope. If he's trying to kill himself with the drugs you absolutely need professional help because you'll just be fighting a losing battle.
Unfortunately, there may only be so much you can do, that he can do for himself, or is just ready to happen immediately. He might still have to hit rock bottom, end up in jail, find God, meet a good woman, or who knows what else to be truly ready to change. Do what you can, but obviously remember there's some things completely out of your control.
Wish you guys the best.