|Do both have different public IPs?|
Are they connected to a router with firewall?
You need to use port address translation (PAT).
Means, for the first one, you can use external port 80 and forward it to internal port 80 to IP of the first one.
For the second, you have to use e.g. port 81 and forward it to the internal port 80 on the IP of the second one.
The original poster should always write the last response !!!
Let us know, if the problem is solved !!!