I do similar every year. When I started there were 9 of us, this year we are up to 15!
I bought a second freezer, and it was a game changer. Means I can do a bit of meal prep earlier in December and just have room for the Christmas Day and Boxing Day basics.
Spreadsheet plans meals for each day, with who is arriving when, then this helps me plan the shopping deliveries....
I book online shopping deliveries for 22nd, 23rd 24th, 27th, 28th. Sounds mad, but the sheer volume of food that we get through each day means it's impossible to store all the fresh food so I let it arrive each day.
Milk, loo roll, kitchen roll, tea bags, bread, biscuits - order a lot, then order some more.
Take away on Christmas Eve is now a tradition as it means I can focus on the Christmas meal prep.
I have no qualms about guests chipping in a bit financially. Each family branch offers a bit and it doesn't in any way cover it but they feel they have contributed and I appreciate the gesture.