They aren't going to show up till end of film.
In comics the X-Men were teens.
Apocalypse Is going to be start of real X-men team.That means Cyclops,Jean,and Storm.It should be pointed out that's not how it was In COmics but was established In First X-men film.
That casting call suggests they are more intrested In getting teenage actors In the roles.
Safe to say they will be 16 In Apocalypse.
There Is no gurante they would even go Into "Phoenix" powers of Jean.
Bryan Singer's approach was Jean's exposure to Magneto's machine expanded her powers.They went totally different direction with Last Stand.Now that trilogy Is out the window and Simon Kinberg said In new future of DOFP that Jean never went dark Phoenix who knows how they will approach Jean's powers.
Apocalypse Is almost sure to focus not on them but on Xavier,Magneto,Mystique.It's possible Beast may get more focus than them.I am pretty sure at some point In Apocalypse Xavier and Magneto will put aside their differences and work together against Apocalypse who with horseman or his army Is causing the disaster film like destrucon SInger and Kinberg have eluded to.
I just don't see them In last film of FC trilogy and last film with the FC big 4 under contract to suddenly see them have them play second fiddle to Cyclops,Storm,and Jean as some seem to think.
As for wolverine I still bet on him being 1 of 4 horseman In film.
Quicksilver could be part of Magneto's Brotherhood If there Is one In Apocalypse.