iPad Mini donated to CoderDojo STEM group, owner unreachable, how do we disable Activation Lock?

I'm part of a CoderDojo STEM group, and an iPad Mini was donated to the group by a family who no longer attends and we cannot reach them. It appears they've created an icloud.com email address named after our CoderDojo group, but didn't give us the password for the account.

We've recently tried wiping the device but it's got an Activation Lock on it that we cannot clear, and we have no way to contact this family. (the iPad was sitting in a box unused for more than a year, none of us even remember which family donated it)

Is this something that an Apple store could help us with? We want to be able to use this for our students but we can't get past this Activation Lock system.