By my count, it's 13, unless I've missed an announcement:
- Pikipek2
- Pikipek3
- Crabrawler2
-
Sea Urchin
-
Sea Urchin2
-
Trap Spider
-
Trap Spider2
- Morelull2
- Salandit2
- Wimpod2
-
Anchor
- Cosmog2
- Marshadow
In addition, there's the Alola Geodude family, and Alola Diglett, bringing the total up to 17. Sidenote: Strange that there are only three "families" of which we've seen no Pokémon at all, again not counting Marshadow.
As for the Ultra Beasts, I actually don't think we'll see all 8 upon release. Gen VII has only two event legendaries (Magearna and Marshadow), which is rather few compared to previous generations (3 in Gen VI, not counting Floette-E; and 4 each in V and IV, not counting BW Zorua, Spiky-eared Pichu or Phione). It would make sense for a couple of Ultra Beasts to be event exclusive too. Or maybe the
back catalog of event exclusive Pokémon is now so big that they're reluctant to add more?