Trouble with Remote Desktop Using Airport Express

Hello!

I have an iMac that I've successfully connected to my employers VPN to then use Remote Desktop to connect to and control my work desktop from my home network. There is a long story, but I've brought my iMac down to my father's house where he has highspeed internet but was not using wireless. My brother picked up an Airport Express and I can connect my iMac, iPhone & iPad to that just fine and can connect to the VPN but when i try RDC I cannot connect to my work computer.

Just for the heck of it I tried enabling my iPhone's hotspot and can connect just fine. I've played around with the airport's settings but can't figure out what would be causing the issue. I suppose it could also be his modem and may look into that if I can't figure this out.

Any help would be much appreciated.

Thanks!