Yes, I think your #1 best option would be to delete all of the collaborators from your Airtable bases, then move everything into a single table in a single base, and then use a customizable “client portal” tool to enable your users to log into your Airtable system, but only be able to view & edit their own records.
These “client portal” tools were specifically designed for businesses that are in your exact situation, and there are 2 “client portal” tools that I know of:
Stacker ($125 per month)
MiniExtensions ($40 per month)
For just one low monthly fee, you can have as many collaborators as you want — and each collaborator is ONLY allowed to view & edit their own records. You would no longer be paying for collaborators in Airtable anymore — you would simply be paying for one of the above 2 portal tools.
So your 11 group leaders would be able to log in, view ONLY their own records, and edit ONLY their own records.
The more expensive option, Stacker, gives you a lot more flexibility & customizability, and also gives you a lot more freedom as to how you can structure your Airtable system. But for simple needs like what you’re looking for, the cheaper option would work perfectly.
If you’d like to hire an expert Airtable consultant to help you set all of this up, please feel free to send me a private message. However, my rates are relatively pricey, so I’m not sure if I would work within the budget of a non-profit.