can travel router connect to hotel public wifi with login and provide wifi hotspot for 3-5 video cams?
Theoretically possible, but many hotels will limit speed, so 3-5 videocams are too much.
And you will be behind double NAT, so the cams won't be reachable from the outside.
Double NAT is no problem (I run camera's on 4X NAT 
"The camera is not reachable from internet, is a very good setup."
Devices deep in your local LAN should take the initiative to connect to cloud or private-cloud service.
GL travel router can setup the needed VPN as well. Again remote deep NATted travel router sets up the VPN to your (private-)cloud service at home. (eg.your router at home, close to the ISP router, and besides or before your own protected LAN subnet.) That home router can be VPN reachable for consulting the VPN connected camera's.
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for IPv6 should not be a problem if it goes via home vpn?