It is rarely a good idea to use multiple bridges.
Learn how to use VLAN on a single bridge.
There is an excellent guide for this:
You may also want to expand a bit on the total requirements of what you are trying to accomplish.
As for your immediate problem:
this firewall rule:
add action=drop chain=input comment="defconf: drop all not coming from LAN" \
disabled=yes in-interface-list=!LAN1
You drop everything for input (also DNS) not coming from LAN1. So that means traffic coming from both LAN2 and LAN3 will NOT get in.
Not unless you change that rule.
Make a new interface list LAN_ALL or so and include in there all ports needed.
Then change that FW rule to use LAN_ALL.
There are other options to achieve the same result.
But in the end I would strongly advice to use the VLAN approach.
Sidenote: about that firewall rule I referred to: it is considered a very bad idea to change a default rule but leave in the defconf comment. Makes it a bit harder for others to see what you changed and what not.
Everything with defconf should be … default config. Once you change it, remove that comment or add your own entry so it becomes clear it’s not default anymore.