Your Inlaws are nuts for suggesting a health issue but you also can flex a little on times occasionally. Like you stare trying to do. Not to say give up the nap, but most kids can shorten/delay/go early on occasion like a holiday without huge adverse impacts.
Not having a two year old at dinner isn't a bad thing.
Fwiw...my son had a schedule like yours too...it was heaven. At four he still naps two hours a day. My mil also thinks he shouldn't nap, and I politely informed her that her control over kiddie naps ended when her son gave them up. She just doesn't get a say in it and I don't discuss it with her. Ever.