How to setup IP alias on bridged interface in Ubuntu

The only way you can do that is from ifconfig (or maybe ip addr add, but i haven't checked it against bridges). if-up.d is okay, but i recommend you use post-up in interfaces, like:

auto br0:0  
  iface br0:0 inet static  
  address 192.168.10.1  
  netmask 255.255.255.0  
  post-up /sbin/ifconfig br0:0 192.168.10.2 netmask 255.255.255.0

You can repeat post-up as much times as you want.

Here is something I'm using, works in Debian 8 and Ubuntu 16.03:

auto lo
iface lo inet loopback

auto br1 
iface br1 inet static
    bridge_ports eth1 
    address  172.17.17.1
    netmask  255.255.255.0
    network  172.17.17.0
    broadcast 172.17.17.255
    post-up /usr/sbin/dhcpd 

auto br1:1 
iface br1:1 inet static
    address 172.17.17.2
    netmask  255.255.255.0
    network  172.17.17.0
    broadcast 172.17.17.255