Your use of numbers as tags is problematic, compared to using the obviously unique seat IDs T1a, T1b, etc. as tags.
I would use this hierarchy for a booking application:
* venue name * seats * "T1a": true * "T1d": true * "T2a": true ...
and for specific events, use
* venue * event info * event seats * "T1a": true * "T1d": true ...
Beware of the difference in encoding of data structures loaded from AI2 into Firebase compared to data added manually via the Firebase console. Also, AI2's Firebase component has been known to confuse dictionaries with numbers as tags with arrays (lists).
(See post 2 at FAQ Section: Firebase)