This will probably boil down to arguing whether Chris is a public figure or not and will also depend on the medium.

Documentaries are an expression of art and fall under the 1st amendment provided they don’t violate any privacy laws IIRC. Anyone can make a documentary about Chris given the extensive knowledge we already have (and will likely continue to have).

Selling reproductions of Chris’ work would probably violate copyright and/or an unlawful use of Chris’ likeness. You would have to get the permission of Chris’ estate to monetize their likeness or use the Sonichu brand.

Chris’ estate would probably go to Cole as the sole survivor, so you would be asking and paying Cole the rights to use Chris’ IP.