Changing dynamic IP addresses

I have tried to find a solution on my on for some time and have run out of time. I maintain a backup server here in my home for some of my family to backup to. I have no trouble porting them through the router. In the beginning it was easy to create a rule for each specific IP address through Comodo into the trusted network zone. My problem is that many of them have dynamic IP addresses that change frequently. This same problem affects me when I travel with my laptop, I also am unable to get to any of my PC’s due to a unknown IP address and not being in the trusted zone. How can I overcome this? I tried using the MAC address of the remote NIC but with no luck. An explanation how to solve this would be great. An example would be even better. Thanks in advance. - DanielOKC