We used to do this. Hundreds of pounds spent and hours of preparation and no one even talked to me. I might get the odd comment from one of the elder family members, but DH's family are insular, all 20 of them.
If I tried to join in, the group went quiet. If I insinuated myself stealthily I had no idea what the conversation was about because it was all ancient family history.
They ate everything in sight (and we provided a LOT- enough for 30-35 people) and drank us dry. They would arrive at 11am and leave in the small hours of the next morning, usually when the booze ran out.
In the end I decided I would facilitate, be polite and charming, but basically act like staff. I put things in the oven and took them out when done, I collected plates, glasses and cutlery, washed and put them out again, I refreshed the food plates, I filled glasses and at 11pm, I went to bed. No one missed me.
Finally, one year DH realised that a) he was the only family member that threw this kind of a party. b) I got nothing out of it c) his SIL was so pissed that she had gone home in our son's size 2 school shoes, leaving behind her leopard print boots and he realised that it was more about the pissup than the family having fun by being together.
We still go out with the whole family, but everyone pays their own way and it's no longer a 16 hour marathon, because it's at a restaurant.