Thank you for your question ArkRoyal!
You can get more builder licenses to have more than one builder site; however, you cannot separate the sites from the builder. In other words, all websites can be accessed for edit through the same builder interface. You can try an alternative to the builder for your client to build their website. Or you can have Softaculous available for them to install what ever builder they want. Sorry for this.
Best regards,
James R