ah black fly season, we also have it in NH, VT and Maine. Not everyone has the same reaction as your family. For some people the bites do not swell up so much. So one strategy is to reduce histamine response but this means starting a month before black fly season, so you inhibit histamine production and the mast cell degranulation that comes with allergies (in this case the saliva of the black flies). BTW prevention (not getting bitten and using effective repellents) always works the best. Topically a poultice of fresh Plantain, Chickweed and Gotu Kola (if you could get it), with a little EO of Lavender would help. Internally an antihistamine (OTC) or bromelain may also help it to resolve a bit quicker, but there is no magic bullet for these nasty, irritating, itchy bites that I have seen,