What is the router make & model?
Possibly they need a x-over connection between the router switch port and the powerline adapter. Most switch ports these days tend to auto-detect this and remove the need for a x-over.
What does the manual for the powerline adapter have to say about connecting to a switch port / uplink port? It probably is automatic, but best to check.
Have you tried both Powerline adapters in the same room? Lots of problems with house wiring can screw up ethernet over mains.
Are both PCs connecting via powerline adapter? Can you test with both connected directly to the router / switch via ethernet? Do they both work? If not, it could be an IP network problem - e.g. duplicate IP address.
When you say they cannot connect the laptop at the same time, what do you mean? Can't connect to the local network at all, or not to the internet?
SD