A.: Your brother's track record indicates that if you decide to lend him $5,000, that money is likely to go out the window. If you can live with that, then OK.
Even if you come up with a payment plan, how are you going to ensure he makes the payments on time? If the house were paid for, you could certainly take back a mortgage, but apparently it is not; otherwise, there wouldn't be an opportunity for another lender to foreclose.
This is a matter of whether you can afford to give your brother $5,000. If not, as much as you might like to help, keep your checkbook closed.