Knowing this, can I create a master key from which it was created?
No.Can I get the next or previous address or address with a key along this path?
Also no.It is impossible to take only the private key at one derivation path and move upwards to a parent key, or move sideways to a sibling key. You can only move down a level to a child key. The only way to generate siblings keys is with knowledge of the parent extended private key. If you do not know this key, then your options would be to either derive it from the seed phrase, or to calculate it based on knowledge of the child private key you already have and the parent extended public key. If you know neither the seed phrase nor the parent extended public key, then there is nothing else you can do.
