Unbelievable50, without knowing more about your dad's condition, history of property ownership, and what is being purchased with his 50% of sale proceeds, it's impossible to give a meaningful response.
I agree that we need more information before we can make appropriate suggestions regarding your situation. It is always sad when younger family members steal from their elderly family members and it is not always easy to stop it from happening.
Hopefully your brother is on the deed. If so, then he owes Dad half of the profit. If there was a Mortgage should have been paid off at closing. Did he sell without Dads signature? If so, you need to talk to the attorney and find out where the check is for Dads half. As coowner I would have thought the profit would have been split. This will become a problem id Dad needs Medicaid within the next five years.
Power of Attorney only comes to use if your Dad is no long able to think clearly for himself.