If my brother died before my mother and he was a beneficiary of my Mom's house, will Medicaid take the house?

Depends on her Will and your state probate laws. It is very possible that the heir's estate acquires her bequest. Medicaid then descends to claim it. A good attorney may have a work around. See one.

If your brother died before he could inherit his share of your mom's estate (she is still alive, right) medicaid recovery doesn't come into the equation, a promise of an inheritance is just words on paper until the estate is settled at some future date. It would be usual that your mom's Will makes alternate provisions if any of her beneficiaries should predecease her.

My sister was also a beneficiary.

She was not on Medicaid. The title was not in my brother''s name. He was a beneficiary.

Was your mother on Medicaid? Was your brother named on the title to the house while he was getting Medicaid, or was it titled in your mother's name?

Who else, if anyone, was named in the title to the house or named as a beneficiary in her will?