Maybe have each couple bring a memory or photo and make a board or album.
When my H was turning 50 his Mom planned a surprise party for him. She booked a restaurant and invited people. She knew that he has always said he would not want a surprise party. I knew it and told her I wasn’t comfortable keeping the secret. I told him and he was so angry with his Mom and made her cancel. Seven years later she is still annoyed he wouldn’t let her give him a party.