If you do 75 miles a week on that MUP then you probably have seen just about every issue they can present a cyclist. Dog on one side, owner on the other with a 20 foot leash strung across the trail, roller bladders with Ipod that will not yield, gaggle of women talking blocking the entire thing, women jogger does a U turn without even looking and gets nailed by a bike, kid trying to learn to ride for the first time without the training wheels. The list is endless.
Kids and cycling a good thing. MUP and cycling with a large group a bad thing. Don't know if you have this option but several of the rail trails in our area are more rural and lightly used which would be better for the kind of group ride you described.