But it is a bit of a nightmare though isn't it when someone says they are a vegetarian and they are coming for dinner 
But then everyone has Foods of Wrongness I s'pose whatever diet they have 
Solution is just to feed thyself what thy likes and stuff the rest of them 
All I can say is our friends don't seem to have trouble feeding us but then we're not the sort to do an audit on every ingredient in what we get fed. If it's cheese we'll assume it was OK, if it's wine or beer we'll just drink it unless we know (sadly Guinness has fish in it)
And when we do Christmas or a BBQ we cook meat for guests. Life's too short to be a Nazi
. . .
I did make a mushroom stroganoff once but we all got hallucinations 
Why are we not shocked?