I have my nephews staying with us this weekend. DH and I have a 10 month old. Just to clarify, there is no way that their parents can pick them up early because they are abroad.
Middle nephew is 6, he is a fussy eater and totally refuses all fruit and vegetables. Other 2 nephews eat anything. BIL & SIL will cook for nephew separately to what the family are eating, so if they have Cottage Pie middle Nephew will be given nuggets and chips. They don’t really force or encourage trying other food as it results in tantrums. They will however ask him to eat the food on the plate, to the point where some family meal times just get centred around him.
Nephew has school dinners at school and teachers report that he eats what is given there.
In the past when Nephews have stayed over I have always cooked meals that I know nephew will eat but leave the vegetables in a bowl on the table for people to add to their plate. So Nephew isn’t served on his plate anything he does not like.
Middle Nephew also likes Craze (or Crave? not sure of the name) cereal but I do not have any because we only eat porridge/ Weetabix. However Nephew will eat Weetabix with some sugar on top, so again, there is something he likes for breakfast.
This has worked fine and I have never had any tantrums or problems with my Nephew in the time he has stayed here regarding food. However this weekend is not going well 
Dinner last night was breaded fish and chips, nephew has eaten this 100 times before. Carrots and peas went in a bowl in the middle of the table. Nephew refused to eat anything. I explained that I am not going to force him to eat but that in this house we only eat fruit and vegetables between meals if we are hungry. He had a strop at the table which we ignored and afterwards all the children had an ice lolly including him as I just don’t want to make food an issue.
Later he cried because he was hungry and I caved and made him a cheese sandwich because I didn’t want him going to bed hungry.
This morning his brothers asked for crumpets and he said he wanted one too so I made him one. He refused to eat it and sat at the table with his arms folded. His brothers started doing what there parents do “Nephew, what’s wrong, you need to eat ect” So I asked them to stop and said “Nephew will eat what he wants when he is ready” so everyone was ignoring the situation and talking about something else. Nephew burst out into a massive tantrum, said he wanted Weetabix. Made the Weetabix, I let his brothers get down from the table. Nephew ate 2 spoons of Weetabix and said he was done.
Now he is complaining he is hungry and wants his lunch now but I have said he must wait until everyone else has lunch.
Can anyone advise me here because I don’t know if I am being too harsh or if I need to be tougher with this. It is hard when it is not your child.