Board Thread:Boruto: Naruto the Movie/@comment-26720308-20150717144006/@comment-945885-20150718112722

None of the articles have given them surnames or said they're part of the Otsutsuki Clan. If you've seen otherwise, it's someone making assumptions and spreading misinformation.

All we know about them is that they're named Momoshiki and Kinshiki, they're the new threats to the ninja world, they attack Konoha to try and steal Kurama's chakra, and they clash with Sasuke while searching for something in Kaguya's castle.

Put simply, they could be members of the clan, but the fact that it hasn't been stated so far makes it much less likely, in my opinion. For now I'm assuming they're members of the same alien race as Kaguya, but not the same clan.