# But I have prayed for you

The word "you" here refers specifically to Simon.

# that your faith may not fail

"that you will continue to have faith" or "that you will continue to trust me"

# After you have turned back again

"After you start believing in me again" or "After you start serving me again"

# strengthen your brothers

"encourage your brothers to be strong in their faith" or "help your brothers believe in me"

# your brothers

"your fellow believers" or "the other disciples"