I understand why you have decided not to invite extended family as this would probably double your guest list. I also can see why you would invite that particular cousin as they live 3 hours away. I am sure your other cousins in both families will understand this. However I am not sure that your fiances sister will. This will cause problems - if I was his sister I would be upset. I think you could possibly reconsider your fiances sister regardless of the situation with his cousin. Good Luck MRS S