Although I am in PA I think I have some relevant answers to some of these questions. In my FRC years as a student on 103 we had many community volunteers, many of which previously had kids on the team, but some who did not. Following graduating and completing my degree I became a, “Community,” volunteer, though it’s not quite the same as an alumni.
1.) Generally they are recruited as co-workers, neighbors, or friends of other mentors or parents of the team. All of 103’s community mentors (as far as I know) had kids on the team at some point, or were alumni, but many had no kids involved for well over a decade.
2.) This really depends on the parent organization (if there is one) and what trust the team has in the community mentors. Some of these mentors became official school employees (purely as robotics mentors) after a number of years so they could still run meetings at the school without the teachers. All school-based programs I have been involved with in PA require FBI background check, state background check, and other checks to ensure the students are safe. Most require school-specific training as well, especially in religious-based schools (similar to YPP).
2a.) See above. Generally an employee of the school needed to be present for every meeting. 103 got around that by making mentors who had been around long enough and gained the trust of the school and team an employee title, often with a small stipend, which gave them full access to the school premises at any time of day (or night). There had to be at least one other adult in attendance, but otherwise meetings could be run without the other mentors (which rarely, if ever happened). Generally if a mentor who was not an employee of the school was the only mentor available no meeting would happen.
2b.) Generally you should have 2 adults in any room students are in. So in your case those two groups would need to meet in the same room if there were only 2 adults available. This is for the safety of both students and adults. Some schools might say 3 people (can be 2 students or 2 adults). This can be a huge grey area (what constitutes a room?) and is definitely something that should be discussed with school administration. So many edge-cases exist on this that are sometimes difficult to completely eradicate with limited mentors. If the team is not school-based there is often no such requirement unless it is created by the team, which in all cases it should be implemented.
2c.) For most organizations I have been involved in there is to be no DMs from Mentors to Students or vice versa except for mentors to their children on the team. That means only group messages or boards. Student-student DMs are often banned too but are much less of a problem, especially if the records can be extracted. Most schools won’t allow official lines of communication like Discord or Slack and rely on Email to have better traceability.
3.) I do not know of any school-based teams that run this way, but it is possible. There are plenty of community-based teams that function exactly this way though since they are not directly associated with a school. FRC 1640, 365, and a few others in the area are good examples of well-run community-based teams that might have some more insight (@Mr_MOE, @carolp, @Clem1640, @Gdeaver)
See if your school might consider adding official employment for community mentors (even with 0 compensation) for a coach position. This is essentially the same thing many schools do with sports coaches from the community. It definitely takes time to build rapport with the parent organization and other parents on the team.