Firstoff, he has a house
That ain't nothing. It's really easy to get "whipped up" into a sense of entitlement, and forget to be grateful for what you do have.
If this house doesn't exist, what would his costs of housing be elsewhere? Realistically. Would landlords rent to him? Would other bankers lend him money to buy a house? Would those costs really be any better? What about the intangible benefits like not having any landlord hassles or having a good relationship with the neighbors? It's entirely possible he has a sweet deal here, and just doesn't make enough money.
If your credit rating is poor, your housing options really suck. Banks won't lend you money for a house unless you have a huge ton of upfront cash. Most landlords won't rent to you at all, because they are going to automated scoring systems to avoid accusations of racism.
In this day and age, there are lots of ways to make money with a property you own. In fact, I believe very firmly in Robert Allen's doctrine: Never sell. That way you avoid the tens of thousands of dollars of overhead costs you bear with every sale. That's pure profit gone up in smoke. Keep the property forever, keep it working for you. If he doesn't know how, learn.
To "get bootstrapped" he can put it up on AirBnB or other services. Or do "housemate shares". When your house is not show-condition, just be very honest and relatable about the condition. Don't oversell it, tell them exactly what they're going to get. People like honesty in the social sharing economy.
And here's the important part: Don't booze away the new income, invest it back into the property to make it a better money-maker - better at AirBnB, better at housemate shares, better as a month-to-month renter. So it's too big - Is there a way to subdivide the unit to make it a better renter or AirBnB? Can he carve out an "in-law unit" that would be a good size for him alone?
If he can keep turning the money back into the property like that, he could do alright. This is what the new sharing economy is all about.
Of course, sister might show up with her hand out, wanting half the revenue since it's half her house. Tell her hell no, this pays the mortgage and you don't! She deserves nothing, yet is getting half the equity from those mortgage payments, and that's enough, doggone it! And if she wants to go to court, get a judge to tell her that.
Is there any cash value in the house?
Not that he's going to sell it, but it's a huge deal. He needs to know how much of his payments on the house are turning into real equity that belongs to him.
"Owning it on paper" doesn't mean you own it. There's a mortgage on it, which means you don't own all of it. The amount you own is the value of the house minus the mortgage owed. This is called your equity.
Of course a sale also MINUS the costs of bringing the house up to mandatory code requirements, MINUS the cost of cosmetically making the house presentable. But when you actually sell, there's also the 6% Realtors' commission and other closing costs.
There's such a thing as an "upside-down house"
This is where the mortgage is more than the house is worth. This is a dangerous situation. If you keep the house and keep paying the mortgage all right, that is stable, and can be cheaper than the intense disruption and credit-rating shock of a foreclosure or short sale.
If sister is half owner, she'll get a credit burn also. That may be why she doesn't want to sell. And that is leverage he has over her.
Liquidating the estate was done correctly, right?
I imagine a "Winter's bone" (great movie) situation where the family is hanging on by a thread and hasn't told the bank the parents died. That could get very complex especially if the brother/sister are not creditworthy, because that means the bank would simply call the loan and force a sale. The upside is this won't result in a credit-rating burn or bankruptcy for the children, because they are not owners of the house and children do not inherit parents' debt.