The first thing you need to do is get rid of the critters. Attic cleanup and disinfection is useless if they are still in residence. Use traps or call professionals to do some heavy eviction before cleaning up the mess.
The next thing you need to do is inspect the insulation. Chances are you’ve already had to tear in there to get at your uninvited house guests, so insulation removal is probably inevitable.
The good news is stripping off all the old insulation means you can be sure there are no more critters hiding up there. It gives you the chance to find any holes through which they can get in and plug it up o prevent future infestations. It also justifying insulation replacement newer and more efficient materials.