Not sure how much experience you have traveling multi-leg journeys with this group, but it is an unenviable situation for you. As others have said - if this is truly life-and-death for your party - you are going to have a hard time finding an airline meal that can accommodate your needs. A portion of your party will need to forego the airline meals and will even have a hard time finding meals in the airports you transit through that can guarantee an allergy-free environment.

At least PHL-DOH and DOH-NBO will be on widebody planes where you won't have a seatmate being served right next to you. You don't have to worry about a full meal service on BNA-PHL, but all F pax will almost certainly offered nuts after takeoff. You might consider booking any empty seats next to you for the BNA-PHL leg. Or kindly request that the seat mate foregoes the nuts (some may oblige, but no guarantees there).

You might consult with the airlines ahead of time. There have been recent cases where individuals with life-threatening allergies are asked to deplane if they raise the matter with the flight crew, as they won't want to assume that liability. Better to work this out beforehand than have any surprises on your day of travel.

Rather than consult an internet discussion board about a specific airline (AA), it may be more prudent to consult with your passengers' doctor and nutritionist, and engage with a travel agent that can help you find the airline that can most closely accommodate your needs.