Tuchel has already said that Gallagher has a place in the team for next season Zat so you can forget him tbh, Gilmour might be a better shout although I'm not 100% sold on him tbh. I don't know about Broja he defo looks good and Saints did try to make a move for him in the winter window but with the slight uncertainty over Lukaku/Werner they may want him back. There will be other young lads in the Chelsea youth setup that I'm sure the coaching team is aware of (they have plenty of players after all) so we will see.
Think Gilmour is a jewel myself, loads of work to be done with him mind, Chelsea would be mad to sell.