Question about users/roles for new plugin.

I am designing a new plugin for a new membership site.

This is my first plugin, so please forgive me if I am asking a question that has been previously asked. I have searched and searched, I could not find any documentation on the roles, other than what the default roles are and what they are good for (administrator, editor, etc).

I have found information that say that roles are what I need to use, but I have also found pages that claimed roles do not (yet) meet an essential requirement I have (see bellow).

No, it is not a contents based site that I could just purchase a plugin for. It is a functionality based site that will require special programming.

Anyway, say I need groups for patients, for doctors, and for relatives.

• Patients can introduce data for themselves only. They can choose which users are their doctors and relatives.
• Doctors can view reports and graphs on their patients. A doctor with no patients (yet) is legal.
• Relatives can view reports and graphs of the people they are related to. A relative not related to any patients should be automatically deleted.

Furthermore, a single user can have more than one group. This is the essential requirement I referred to above, and the reason I am asking this question.

Can I do this with roles? Do I have to design my own code?

If I actually have to write my own code, I would be willing to donate my work for the core for others to benefit.

I am currently designing the plugin, so it is the correct time to make such design decisions.