My non legal thought is that if you are also a statutory road association, "mandatory" membership is limited to properties that benefit from the road(s), which generally means deeded access. If it can be argued that these properties benefit legally, I would think they could be included, otherwise, membership of owners on these roads would likely be optional or voluntary. I don't know how non statutory associations bind their members. Before we became a statutory association, less than a third chose to pay.