Hi,
If the 2nd site send direct DNS requests directly to the Umbrella cloud (traffic is source from a different NAT IP address to the other site), then each site would require a separate VA, Umbrella recommend allows deploying 2 per site for redundancy.
https://docs.umbrella.com/deployment-umbrella/docs/3-deployment-guidelines
As long as the Android devices are pointing to the Umbrella VA appliance IP address for DNS resolution that should work fine. The Umbrella Roaming Client only supports Windows and MacOS, so you cannot install the client on Android.
HTH