Question: who is related in it's always sunny
Answer: The series follows `` The Gang '' , a group of five depraved underachievers : twins Dennis Reynolds ( Glenn Howerton ) and Deandra `` Sweet Dee '' Reynolds ( Kaitlin Olson ) , their friends Charlie Kelly ( Charlie Day ) and Ronald `` Mac '' McDonald ( Rob McElhenney ) , and ( from season 2 onward ) Frank Reynolds ( Danny DeVito ) , Dennis ' and Dee 's legal father .