If my fiancé and I decide to go to his aunt's wedding, do we have to invite her and her husband to ours (a few months later) in return? Ours is going to be small, with just immediate family.
There is no reciprocation rule. Plus, if you invite this aunt and her new hubby to avoid hurting their feelings, you'll run the risk of insulting other relatives, who won't understand why you couldn't make an exception for them, too. If you want to go to your future aunt-in-law's wedding, you should, but your fiancé should give her a call to explain that your wedding is going to be super-small, with only immediate family present. Smooth feathers by inviting them to a casual celebration, or get together when you get back from your honeymoon.