the hearts of the saints have been refreshed by you

Here "hearts" is a metonym for a person's emotions or inner being. This can be stated in active form. Alternate translation: "you have encouraged believers" or "you have helped the believers" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-activepassive)

you, brother

"you, dear brother" or "you, dear friend." Paul called Philemon "brother" because they were both believers and he emphasizing their friendship.