Yes, they are. But we've seen them as a pair already once before in the CC v Brighton. The did not really have the same understanding with each other as they would have with one of the starters. Lets hope they've worked on that and keep it tighter. Chelsea are much better than Brighton in the CC. Regardless if they are very capable backups, they are still a slight dropoff from Saliba and Big Gab.
Gonna need a big game from everyone.