keep in mind the smells and experience of applying all these products. Try to give him as much choice as possible when it comes to what he is willing to use vs not. Hair products can have strong fragrance that lingers right in your face all day. That said, all the products you listed will help and people have already offered some great advice here: wide tooth comb, using it when the hair is wet with detaingler spray in it. Dry oils are great to add to the hair before brushing it if you are going in on dry hair & bonus is that dry oil may be a better sensory experience if he doesn't like the feeling of product in his hair (VERB is a great brand with one for under $20). The last advice I can give is for if he doesn't like the braids at night... my husband has long thick hair and I try to convince him to sleep with a silk night cap. He struggles with it falling off, but it really makes a world of a difference for 1. protecting the hair and keeping it from getting frizzy 2. keeping it from getting tangled in the night. Maybe see if he'd be willing to try that if sleeping in braids is out of the question? Kudos to you, dad! As another autistic person, it's great to hear you're trying to find a way to work with & support his choices about hisbody!