I have been married just at the 5 year mark. My second marriage, her third. I have 2 step kids, boy 26 and a girl 23. The boy moved in with us just last August. He comes and goes, stays mostly at his girlfriends house. He asked to move in with us, not my idea. Uses the 2nd bedroom for his computer, clothes etc. seems not to contribute anything to this household at all, when he stays overnight, plays on computer all night long. Mother doesn't see anything wrong at all. He will be graduating to become a RN after all these years of hemming and putting off what kind of major he wanted to pursue.
The problem is, I wanted to charge him partial rent to make him responsible, not like his other cousins who stay at home and not work at all, (29 years old male, parents encouraged their boy to quit job at bank) but me bringing up the kids causes rift with my wife. She feels kids are perfect, but I see beyond all of that veneer.
I really don't like the kids at all, they never lived with us and now they come over and it just bothers me a lot. What would you do?

Your stepson, at age 26 is an adult. He needs to begin acting like one. He needs you and his mother to push him out, not provide a room for him. It would do him good. I'd present it that way to your wife. Have you seen the movie "Failure to Launch"?

Your anger towards his behavior is not part of the deal though. If there is a rift between you and your wife because of your resentment of her differing values, your resentment of his presence, that is your stuff.

The heart of the matter is good parenting. You and your wife are a team. Mostly you share the same goals. When you are in disagreement, how do you solve that problem? Her son's behavior is not really the problem.