You will need to remove the names from both Butch and Sundance. (Were those the two people?) Since the pictures would no longer be together in say the People>Butch album, I'd go to that album that has both of them, select them all, and put them in a regular (not people!) album named Butch&Sundance. That way, they're easy to find after you remove them from their Butch album.
In People>Butch you can select all, and then more (...) and choose "These are not Butch." Then go to your Butch& Sundance Album and find all the pictures of Butch, and name them Cassidy. (You have to use new names different from Butch or Sundance, because it already has wrong characteristics for those names.) Then find all the pictures of Sundance and name them Kid. You should after a while have People>Cassidy and People>Kid albums.
I think that after a time, you may be able to change Cassidy and Kid back to Butch and Sundance.