Pellegini and Cordon are rebuilding a defense which was very poor last season. They need a lot of changes but don't have much money unless they sell someone like Fekir for big money but I'd guess they'd prefer to keep and build the team around him.
Montoya is a solid, more defensive backup to Emerson who should still remain a starter and play a lot if we won't bring him back to sell him - which would be stupid imo.
And Bravo will most likely also be a backup. Joel Robles wants to leave since he doesn't want to be a backup and there were rumours they want to use a current situation at Valencia to bring.... tadam drumm roll please... Cillessen.
Rui Silva from Granada is another option.
Speaking about our ex players they're supposedly looking to offload both Bartra and Tello. Serie A teams are interested in Bartra and I've read they've received a 10m offer for him from Sampdoria IIRC. They've already sold Zou Feddal to Sporting Lisbon and might also sell Mandi so Sidnei could be the only CB who'll stay and they'll need to bring at least two if not three new CBs.
Betis is one of the clubs following Malang Sarr but he'll probably end up in a bigger team. Martinez Quarta (River Plate) was also linked to them but again, many clubs are following him. Cordon has a good history signing South American CBs from his time at Villarreal with the likes of Godin and Musacchio so we'll see.
In midfield Pellegrini wants Erick Pulgar but Fiorentina seems to be asking for too much money. Raul Guti (Zaragoza) looks to be a cheaper alternative option. Valencia also showed interest in him.
There probably won't be too many changes in attack. There is interest from EPL clubs in Loren Moron but I guess they'll want to keep him and at the same time also hope Borja Iglesias will have a much better season. In case they'll eventually sell Loren then Luis Suarez (not ours) could be an interesting option but he might be a bit out of their range if Watford will decide to sell.