Of course. I’ve updated my initial diagram. If more details are needed, I’m happy to add them to the diagram. Config of my both routers is also posted in my original post.
Here is InternalRouter Quick Set options:
And InternalRouter routing table:
Yeah, so here is the scoop,
Why does your bridge have an IP address in both cases.
Remember its far simpler to keep everything vlans so every subnet should be a vlan.
What subnet does your bridge provide…
What other vlans do you have.
vlanX=home
vlanY=Guest
what is bridge subnet user for??
or do I have this wrong and you only have one subnet for everything??
Its a home network, so it’s just one flat /24 network.
My bridge has an IP, because otherwise I was not able to connect to it and if I remember correctly it was not getting IPs from BorderRouter DHCP server. It was set up this way long time ago. It was working, so it was good enough.
There are no other VLANs, no other subnets.
I want to create guest Wi-Fi at home, so that is way I embarked on this “odyssey” 
Well a guest wifi usually means a wifi that you want isolated from the rest of the network.
Unless your AP can create a guest wifi and futher that its isolated from:
a. wifi users on the regular WLAN (not the guest one)
b. all wired users on the same subnet.
You will need two things.
a. an access point that can handle vlans OR
b. extra access points, one for home and one for guests.
I am not familiar enough with MT wifi to know how to accomplish the isolation as required.
But adding a vlan for guests to both MT is relatively simple and will accomplish what you desire.
Which brings us back to the original conversation, how many subnets do you want.
a. one for home wired and wireless
b. one for guests wifi
c. any for video cameras
d. any for media
e. any for iot devices (thermostats etc..)