Based on this article
https://www.sport-english.com/en/news/revolution-planned-for-barca-b-next-season-6835850
I can see this team for Barca B next year:
* = promoted
GK: *Iñaki Peña, Jokin Ezkieta/Adrián Ortolá (one is sold)
CB(R): Santiago Bueno (from loan), *Óscar Mingueza
CB(L): Jorge Cuenca, *Chumi Brandáriz
RB: *Mateu Morey, Dani Morer/Sergi Palencia (one is sold)
LB: Marc Cucurella, *Juan Miranda
DM: Oriol Busquets, *Monchu Rodríguez
CM/DM: *Riqui Puig, *Jandro Orellana, Marcus McGuane
CM/AM: *Álex Collado, Àlex Carbonell (bought back)
CF: *Alejandro Marqués, Rafa Mújica (from loan)
RW/RF: Carles Pérez, Ballou Tabla
LW/LF: *Abel Ruiz, Mohamed Ezzarfani (from loan)
So all these will either be sold or let go (or promoted) - a lot:
GK: Adrián Ortolá
OR Jokin Ezkieta, Sergi Puig
(currently on loan), Alberto Varo
(end of loan)
CB: José Antonio Martínez
(end of contract), Rodrigo Tarín
(end of contract), Adrià Vilanova
(end of contract), David Costas
(end of loan)
RB/LB: Sergi Palencia
OR Dani Morer, José Luis Trápaga
(currently on loan), Samu Araújo
(end of loan)
DM: Ferrán Sarsanedas, Martin Hongla
(end of loan)
CM/DM: Alasana Manneh
(currently on loan), Braima Fati
(currently on loan), Christian Rivera
(end of loan)
CM/AM: Carles Aleñá
(promoted), Iñigo Ruiz De Galarreta, Vitinho Carvalho
(end of loan)
CF: Marc Cardona
(end of contract), Jérémy Guillemenot
(currently on loan)
RW/LW: José Arnáiz
(either promoted or sold), Juan Cámara
(currently on loan), Matías Nahuel
(end of loan)