It sounds like the apartment’s wifi is only allowing a single mac address to be used when connecting over wifi. If that is correct you may be able to use mac address cloning or spoofing for the second and third , etc devices. Basically, this is what the wired router is doing currently with NAT. Maybe there is a travel router that accepts a wifi signal for its WAN input and broadcasts its own wifi signal that all of your devices can use. This will be slow, much slower than what you have currently. Best case is if the wifi WAN input is over the 2.4 GHz band and your router only broadcasts over the 5 GHz band.
what about using cell service for the internet connection ?