Is it recommended for a small organization to have more than one Owner role in GCP? My Google results seem to be too broad. Please could anyone advise me on that?
The owner role is a legacy role and has too wide range of permissions. It's not recommended to use it but it's the default role with your create a project.
In your question you talk about Organization. I don't know what is it, but there 2 cases:
In both situation, the principle is not to loose the control of GCP project in case of owner credential loss. That way, I recommend to always have a backup, but not especially another OWNER user.