We had most of those at one time. My son started reacting to hemp. It turns out all hemp is produced with sesame (rotated fields and the like) which crosses majorly with tree nuts. I wouldn't do hemp with a tree nut allergic kiddo knowing what I know now. My son is sesame and tree nut allergic/anaphylactic now. Sesame is a bear to avoid.
I used to use rice protein powder but I wasn't worried about cross and knowing what I know about cross with nuts I'd be very careful with protein powders and certainly call about shared equipment. Beyond that, protein powders are all going to have free glutamic acid and so I wish I hadn't done that back then from that standpoint though your child clearly needs the protein so if this is your only alternative and you can find a safe one of course do it.
Look at his actual protein needs (in grams) and you may find it's lower and more doable than you think. We used spelt (sprouted/sourdough) and quinoa and similar decent protein grains, avocado, and meats. He was a very poor meat eater when young. I can tell you what I did do in that situation when he was younger but it's gross. I pureed chicken breast into stuff like smoothies and sauces. You need a strong base to disguise it but low fat meats like that puree well and chicken breast has a high protein content and a relatively low amount of taste. As he got older I just explained that he had to get enough protein so he needed to eat x amount of the meat served. Hard times--really they were. I was so thrilled to get dairy back.

Calories can be tough with those restrictions as well.
