Can R/r in Musig be derived from only seeds and message hashes?
The construction you're suggesting will likely work as long as you don't sign more than one message. By effectively choosing the R points ahead of time, you've constructed a single-show signature.

However, the derivation you're using for the different R values is pointless. It's not enough that you don't reuse R values; you can't use multiple related R values either. All the R values you are constructing are related through a single linear equation. That is sufficient for an attacker (who knows about the relation) to derive the private key from seeing two signatures.