Hi there.
It sounds like your working through the best way to organize your data. I’ve mocked up an example data diagram that may point you in the right direction.
You basically have 2 top level data tables. List of school PTAs and a list of volunteers. A PTA can have many volunteers and a volunteer can serve at many PTAs. In order to model this “many to many” data relationship we need a 3rd data table called PTA roles. This relates a many volunteers to a many PTAs. To handle time logging. We have a 4th table that has a volunteer an their role and how much time they served.
The lines in this diagram represent Reference relationships between the tables in your app. The field with the crowd foot attaching to its side needs to be set as a Ref column type in the app and have that Ref column point to the adjoining table as it’s source data.