Yes it is as I thought, in that case you cannot connect your containers to the br0 bridge because that is a layer 2 device and each container NIC will then present its own MAC address onto the external network, which will then be filtered by the upstream ISP.
Instead take a look at using the routed NIC type as this is specifically designed to allow static external IPs to be routed into a container while still using the host’s MAC address for external connectivity.