So i have set up a ubuntu server to do: samba, ssh, and sftp. SSH and sftp are both done through openssh using different users for each service with different settings by using the Match USER option. I would like to have both users (ssh admin user & sftp user) to use different rsa keys to login. I can force them both to use rsa keys but it is the same key for both users. Is there away to set different rsa keys for different users?

Bonus question: How do you convert id rsa key to ppk for filezilla in the terminal? (I forgot to write it down)