My brother can no longer afford or be safe in his home. His sole income is social security. Can Freddie Mac take his social security.

What lender holds the mortgage? Is he on SSI or SSDI?
Even after you answer those, it gets tricky, if he no longer lives in, or is about to leave, his residence. At that point some things will change.
This is a topic that needs a lot more details, and his best bet is to talk to a town social worker.
Houses do get seized and sold to pay for state costs like nursing homes under Medicaid, etc, so you need to act quickly.

Joypulv, "Freddie Mac" is the Federal Home Loan Mortgage Corporation, which, I assume, is foreclosing the brother's mortgage. No, I believe the brother's Social Security is exempt from execution, even for such a mortgage foreclosure deficiency judgment.

I know, but wondered if the mortgage had been sold.
SSI and SSDI are treated quite differently in all aspects.
And the brother is leaving his residence. The house is now just an asset, not a home.

But FHLMC isn't in the business of financing nursing home care. I'm guessing that this question has to do with mortgage foreclosure and you suspect it may be about Medicaid reimbursement; we really need OP to come back and un-confuse the issue.

True, I'm mixing separate issues together.