You could always wrap up a box of trash bags...hint...help clean up after the party? Or wrap up an apron. The recipient helps clean the kitchen/helps with the dishes. (Do you have one that was your Mom's? This will also make it a personal, special, not so "gag" gift and can be passed around year after year.)
How about buying children's books for each family member based on their likes or hobbies? A baseball story for the brother, etc., who is wild about the game? Ballerina book for the dance lover, etc. After the party, these books can be donated to Toys for Tots or another organization for needy kids. (Games and toys work as well).
Sounds like a fun party. Sorry to hear about the loss of your dear Mom. Holidays are never easy, especially the first year after the loss, but you are definitely on the right track. Enjoy!
Anita