An informal "brown bag" train hobby group that meets over a McD meal (or something of their own making) in rotation at the homes of group members/hosts sounds great. Talk trains during mealtime, and then adjourn to the train room for a work session on that member's layout or an operating session. Some hobbyists would probably be satisfied with that modest level of engagement with little or no money involved. Others seeking participation in a grander enterprise may gravitate to an organized train club with more to offer (and more to take -- dues, time, energy, fund-raising, and investing creative thought in organizational development).
Trouble is ... humans are political animals by nature and issues may soon arise even in a small group. However, it's supposed to be about the fun of sharing the world's greatest hobby. New group members should demonstrate a suitable hobby-related purpose, eagerly participate in group meetings, and host an occasional meeting as expected. Anyone could signal waning interest (or they "got what they initially came for") by simply not coming to a few meetings and quietly dropping out without going away mad or stirring up a revolution.
Mike