Are other co-investigators or collaborators allowed to attend the RF meeting along with the investigator?

Yes. Any researcher approved by the investigator is allowed to attend the meeting.

Are projects discussed at more than one RF meeting?

Normally projects will be presented at only one RF meeting.  However, any investigator can request a second meeting, if they so desire.

Can an investigator pick an ad hoc subject expert to join the RF Team members at a meeting?

No.  If an investigator can identify a potential ad hoc expert as an RF Team member, then it is expected the investigator can arrange for a personal consultation with that person.