Regardless of products used Pete, I would advise in all of your dealings and correspondence to only state that you will be cleaning and
treating the fabrics in accordance with the manufacturers instructions. NEVER say you will remove the allergens.
The most important part of this job is going to be the pre-vaccing. Go overboard with it. New bags and clean HEPA filters. When everything looks as clean as you can get it, vac it again
Close the door and open the window for this, obviously keeping sensitive people away from the work area. A return visit to vac again upon completion of drying wont hurt either.
As for products, if someone is sensitive to allergens, my own preference is to leave the fabrics as free of chemical residues as possible. For this reason, I would prefer to use a colloidal solution such as Nemesis or M Power with a fresh water rinse. A good dwell time, say about 20 minutes, is essential.
I'm really out of touch with detergents these days, so others will give relative advice on these. Crystal Green though is a problem solver and not appropriate to your problem.
Safe and happy cleaning
The Ken