I can understand your difficulties as your son suffers from multiple food allergies
Many food allergies, such as egg and milk, are outgrown during childhood whilst allergies to peanuts, nuts, fish and shellfish tend not to go away.
The issue weather he is allergic to soya or not is unclear.
You need to see an allergist & an experienced dietician.
Kids with a history of a previous severe reaction should be given self-injectable epinephrine
) and a written emergency plan in case of accidental ingestion .
There is no consensus as to whether food allergies can be prevented. Several authorities, however, recommend delaying introduction of major food allergens to infants from allergy
prone families. Recommendations include promotion of breast-feeding with maternal exclusion of peanut and nut products from the mother's diet and delay in introducing major allergenic foods: cow's milk until 1 yr of age; egg until 18–24 mo of age; and peanut, tree nuts, and seafood until 3 yr of age.
Hope you find this information useful.