Twice in my life I arranged for a close relative who my (different) partners had not seen in years, to secretly fly in as a birthday present. I hid them both in the closet and told the recipients that their present was in there. Easily the two best gift reactions I ever experienced. I highly recommend it to you if you are in a position to pull it off.
No further explanation needed. All comments welcome.
That is a cool idea. My wife once flew back to Indiana, put on a disguise, and then went to a restaurant where she knew her family would be found a way to engage them in conversation. Afterwards
she went to the restroom, washed off the makeup, changed clothes and asked them if she could join them. She fooled everyone except her older sister who was in on the surprise and everybody loved it.