You can message your group from within your group mini site using the communication link, shown below:
You can create data lists, enabling you to manage your members.
Add a name to the "Create New Data List" box (e.g. Wokefield Park 02/02/2015) and click "GO". The list will appear below the box and if you click "View Data" you will be given the option to manage data on the list e.g. who has paid, cancelled, refunded, attending etc.