Growing up, my family had two very different food allergies to deal with. My brother the oldest was allergic to eggs and shellfish. His egg allergy came to light in Walt Disney World at an all you can eat pancake breakfast and his shellfish allergy was discovered soon after that. My peanut and nut allergy was discovered after I ate a cracker smeared with peanut-butter.
Our parents were faced with a bit of a conundrum, we both had different allergies and different dietary needs. They needed to decided if they would rather restrict us from eating our own allergens or keep both sets of allergens out of the house and away from both of us.
In our house my parents opted to keep all allergens out of the house, that meant no eggs, shellfish, nuts, and peanuts were allowed in the household. In my personal opinion this led to less resentment and yearning for a certain food/treat we may not have been allowed. I never had any resentment towards my brother or parents because I never saw them eat things I wasn't allowed to eat.
I recently became a mentor on a board for parents and children with newly diagnosed food allergies. The most arguments and complaints children had was watching their sibling eat treats and snacks they were not allowed to. The parents, stuck between a rock and a hard place had to choose between denying one child or the whole lot of them. I can understand the stress of the situation but it is my own opinion that it is unfair to exclude someone, especially if they are in the same family.
Think of it as saying one child gets to go to Disney as the other watches, ok maybe not that great but still it hurts.
Denying one child food but allowing others builds resentment towards their siblings as rational as you may think you are, every gets upset when they're told they can't have something but someone else can.
If someone in your house has a severe allergy its only safe and fair to keep that allergen out of harms way, because after all your home is your safe haven it should be where you feel most comfortable. To this day my parents still keep our food allergens out of the house even though we've been since moved out. I do realize that this is a bit extreme but if you spend 20 years without a certain food I suppose you tend not to miss it after awhile.
The parents and children I mentor still face this battle everyday, and as children get older, they don't get any easier. My best advice would be to talk with them as a group about what they want. If both parties feel comfortable maybe work out a system where they can go eat the allergen outside of the house if they wash their hands/clothes etc. and vise-versa. The most important part is make sure everyone in the situation feels safe and respected.