My mom is a Catholic and my dad is a Catholic/Buddhist (yes, both) but he does this Buddhist ritual more than once every year. In it, my family prepares a bunch of food and sets it on the table(s). After so, my dad waves a stick that's lit on one end(I don't know what it's called. An incense stick?) and asks for our deceased family to come and feast on the food(I believe he's praying to Buddha). Whenever he does this, however, he almost always call for my sister and I to take part in asking (Buddha?) for my deceased family to come eat the food. My mom says that it's only a thing of remembrance though. I don't believe that my deceased family actually comes to my house and eats the food, and I don't believe that Buddha can do any of that stuff. I only do it because I'm forced to and if I don't do it, my dad will most likely bring trouble.
So I’m wondering if it’s a sin to take part of this even though I don’t believe in it or anything like that? If it is, then could you also give me advice on what to do?