It can be difficult if both have an established habit, & you may have to ensure that they can't get to wall paper for a whileunless you are supervising them & can stop it as soon as they start. Also they tend to strip any loose bits.
Take it from me, it's a disaster to let a rabbit see you decorating & stripping off wall paper. They see it as a fantastic game & "what's sauce for the goose is source for the gander" as far as they're concerned.
If they're actually eating the wall paper they may be craving woody fibre. You can help this by giving them small twigs to chew, or safe tree leaves in with their hay. After you've reprimanded them for wall paper stripping, immediately offer them a twig (=this is what you chew on).