Parent / Children User

Is there a plugin or something that will allow multiple users (parents) to be able to have a client list (children) and keep the data separate?

For Example: Bob has 5 clients and John has 62 clients, I do not want Bob to see Johns clients or vice versa.

would this be accomplished by multi sites? so my core site would be replicated to each Bob and John, yet their clients will remain separated?

or is there an easy way to do this? It will be important to allow Bob and John to customize their forms and info about their business.

if multi site is the best way, is there a plugin that would allow a new site to be generated and created when a new “parent” signs up on my site OR do I have to do it manually?

Thank you in advance for the clarification