Whom did Jesus heal of a fever at the home of Simon and Andrew?

Answer: Simon's mother-in-law

Jesus took Simon's mother-in-law by the hand and helped her up; the fever left her and she began to serve them.

“As soon as Jesus and His companions had left the synagogue, they went with James and John to the home of Simon and Andrew. Simon’s mother-in-law was sick in bed with a fever, and they promptly told Jesus about her. So He went to her, took her by the hand, and helped her up. The fever left her, and she began to serve them.”— Mark 1:29-31 (BSB)