I'm with AHG but I do short emails about just one topic each.
I don't pester or remind. If they don't sign up by the date given, they are not going. If required paperwork is not in, then they cannot stay for the meetings.
Once I raised my expectations of parents and stopping allowing myself to get frustrated it is a far more enjoyable role. Put the responsibility on your parents if they want their daughter in the troop then they'll do the work necessary.