The Tyson Fury fight is on BT Sports Box Office Pay Per View and not Regular BT Sports.
If you Google the fight there will be a number of ways to watch it (unfortunately not on NOW UK or NOW Republic of Ireland with the NOW Sports Pass extra Membership for NOW ROI customers).
No. If you don't subscribe to BT you can buy on a one-off basis by installing the BT Sport Box Office app on your Apple, or Android device. You can then watch on that, or use Airplay, or Chromecast to watch on your TV if you have these options available.