Okay well just like the license says one install per domain.
Redirection from 3 names if fine. Cause remember you will be redirecting 2 names to the one. Photopost will only be running on one domain. The one you install to.
Once they are directed to the program it will show the one main not the ones redirected from.
However you may not install the software 3 times one install for each domain name. There can only be one domain name and one install per license.