All of this could be done without blockchain. Once they sign a signature with their private key they can't unsign it later. Once you attest something you cannot un-attest it.
Just make the public key known and sign things. Please stop shoehorning blockchain where it doesn't belong, especially when you aren't even giving any examples of things that blockchain is doing for you with 100000x the cost and complexity, that normal crypto from the 80s/90s cant do better.