Slight non-Christmas related hijack alert*
A similar thing happened to me once Mega. It was BILs birthday and SIL wanted to throw him a family party but she hates entertaining and having anyone but her own parents in her house-- so she asked us if we would host it at ours, as her house was too small apparently.
She asked me to do a lunch buffet for about 15-18 people and she would give me the money for the food. She couldn't actually help me do any shopping or cooking or cleaning, because she lived a two hour drive away. They wanted to arrive at 10.30 am so they could leave home early and miss the bad motorway traffic, but I said I couldn't really cope with having them there that early and could they please arrive (SIL&BIL, her parents, siblings and DNs etc all en-masse) at nearer to 12.00, as I couldn't get the food done and manage to put the hoover round etc., and get myself looking decent if I had a houseful by 10.30am. Not an unreasonable request, I thought.
So they all turned up at about 12.30-12.45 (so late then
) and said they couldn't possibly eat a thing because they'd all only just had a huge Little Chef breakfast.
Because I asked them to come a bit later and they'd decided in advance that they would be stopping for breakfast, so it was my fault basically, that their breakfast had been a very late one, by messing with their plan to arrive at my house at the fuck of CRACKING DAWN.
So the lunch buffet sat there going limp, and being conspicuous by its vast quantity. And to add insult to injury she'd asked me to make a dessert, which no-one was then allowed to eat, because her mother had decided to make BIL a cake and 'she's gone to a lot of trouble' and it wouldn't be fair to her if the children all filled up on my pudding and didn't have room for her mother's cake.'
So I know how you feel. Like you want to run out into the woods and scream like a lunatic at the moon. 