Can a single physical interface act as a “slave” for multiple bridge interfaces

why do you need an alias on br1:0? this might be in the way there
besides the alias, the idea is to use the following scheme:
eth0->br0 <--VM's tap device
the host should be able to use br0 as it's IF and the VMs will be using the tap devices as virtual NICs plugged into a virtual switch (which br0 effectively becomes here)

the same goes for every network of course, so for eth1, you'll have to set up an br1, and bring up the VMs to be plugged into br1

As far as I understand Debian network configuration infrastructure, using brX.YYY should not work as it would create a VLAN pseudo interface "above" the bridge, for which support has just begun being added to the kernel: https://lwn.net/Articles/513710/

Here is the kind of config I use:

# Bring up physical interface
iface eth0 inet manual

# Create VLAN interfaces
iface eth0.10 inet manual
         vlan_raw_device eth0

iface eth0.20 inet manual
...

# Create bridges
auto vmbr10
iface vmbr10 inet static
        address  10.10.10.81
        netmask  255.255.255.0
        #gateway  10.10.10.254
        bridge_ports eth0.10
        bridge_stp off
        bridge_fd 0

auto vmbr20
iface vmbr20 inet static
        address  10.10.20.81
...

If you want to use agregated/bonded interfaces:

• bond the physical interfaces
• create the VLAN interfaces on the bondX interface (bondX.YYY)
• use the bondX.YYY as bridge_ports