Not having any sources, other than this forum, check the following on this forum: Benjamin BREWER was born 24 Apr 1755 in Fayette Co., PA and died 06 May 1834 Salem, Washington Co, IN. He married Catherine MELLENGER on 18 Mar 1781. Benjamin and Catherine's children were Hannah (m Rev George MONICAL), William (m Magaret HOLMES), Samuel, Peter, John (m Elizabeth COOLEY), Catherine (m Charles NUCKLES) and Benjamin.
This would indicate that it was William Brewer who married Margaret Holmes, not his brother Samuel.
I have more on Benjamin and Catherine Mellenger Brewer.