Yes
Yes
The ISP blocking port 80 is strange, so I am assuming it is blocking incoming connections to port 80 on your public IP. Being that you have embedded webservers I'm assuming you don't know how to log in to the embedded devices, and change things.

To redirect another port to the embedded devices you will need to add a configurable router or computer between the devices and the Internet (If I have you topography correct). The easiest way for me would be a basic Linux installation, with a few iptables firewall rules. Should take me an hour.

If you have no Linux experience this might be a day's worth of work. Alternatively you can drop in a computer with MS Windows on it (if you want to go the less functional/expensive way). Unfortunately I have no experience with MS Windows firewall applications. It might take you a day just to decide on a firewall application

I have a firebox edge router, which I forward out other ports already.
I just can't figure out how to redirect say port 81 to the webserver which is port 80.

can you put the port forwarding interface screenshot of your router here?

here is a screen shot of my firewall port forwarding

this is probably the wrong interface
do you have anything that mentions virtual servers, port forwarding, redirection etc?

that is the port forwarding on the router.
thats where I have forwarded out all my other ports from.

http://portforward.com/english/route...outerindex.htm
can you find your router here?

here is my router
http://www.watchguard.com/products/x55e-w.asp

couldn't find any proper documentation on the site. maybe you should try to call them for support