Inlaws and child's allergies/nutrition

[Sumosally]

My inlaws are very helpful and generous, but are completely clueless when it comes to nutrition and particularly food allergies. They will allow eldest dc to disregard everything on her plate other than the bread and ketchup and if she eats one morsel of vegetable when I'm trying to get her to eat more, they will proclaim loudly that she's wonderful for taking a bite of carrot, now that's plenty of the good stuff, so where's the cake and biscuits? My MIL is very, very undermining when it comes to their food.

More worryingly, both DCs have allergies (different) and I have written down specifically what they can each eat. This has still led to DC2 being given an allergy food whilst in their care as they were too arrogant to check the packaging saying that it "shouldn't contain" any of what it did. I then said I would be sending the dcs with packed lunches which seemed to offend them as MIL enjoys baking allergy free treats for them (when it suits) she is also a control freak.

We went out for much with inlaws at the weekend and MIL tried to give DC2 food from her plate. I said not to as I wasn't sure if the vegetables had been coated in butter (dc has a dairy allergy). Within 5 minutes, MIL tried to give DC a carrot from.her plate. I again had to repeat myself then "no, she can not have that." DH actually shouted at MIL and turned heads in the restaurant. He was furious.

I'm not sure why they are so incapable when it comes to their food, but its making life very difficult. Despite DH witnessing this he still protests that his parents are capable of dealing with their allergies.
I'm not sure...
I can't understand it. Is this ignorance, arrogance or sheer antagonistic behaviour on behalf of MIL? They are brilliant in many other ways, but the food/allergy management when DCs are in their care is beginning to cause a rift.
Any ideas?
Just to add that the allergies are non-ige, but the effects of the allergies on their digestive systems are severe.

[MustardScreams]

Yeah they wouldn’t be spending any time with my children without me there until I knew for certain that they took allergies seriously.

I despise people that do this, think they know better and actually cause harm to a child because they want to be right? Or whatever.