Considering it's release date, I wouldn't be worrying about the momentum of films coming out the previous month. Trolls comes out Nov. 4th, so animated film-wise Moana will probably take the momentum from that. (Though Fantastic Beasts and Where to Find Them could throw a wrench in things since that comes inbetween those two.)
For Sing I would be worried about the momentum of a film that comes out five days before it....Rogue One. That's a juggernaut IP that get's a wide audience, add in it's looking to be the anticipated film for the end of the year, that's hard to counter.