not much you can do if you cant forward ports on your router (ipv6 is the same as ipv4 just longer) so ports still need to be forwarded. only other thing i can suggest is try setting the pi outside the firewall in the router set it as a virtual server ( long shot but.it.works sometimes) as for ipv6 if yoir router dosnt support it there nothing you can do. mayne check for a router firmware update?
No, IPv6 doesn't necessarily require port forwarding since it doesn't require a NAT. First half of a v6 address is the network ID (per internet connection), second half identifies a device using its MAC (with FEFF inserted as per SLAAC) or using a random value (more privacy). Of course, ISPs are free to do whatever stupidity they want, although I wouldn't expect it.
This tool can check if a specific TCP port on v6 is accessible. Provide your pi's IPv6 address (should be global, not anything in the form fe80:*)
