Tell me.
To me, it belongs to the original timeline.
I think that the movie is a good and fun popcorn superhero flick, they just should redo the digital claws sequence in the Hudson family's bathroom.
I don't see anything wrong with it, quite frankly.
Emma Silverfox and Wade/Weapon XI are just reinterpretations. Weapon XI was scary and frightening. Who cares about having a comic book faithful adaptation? Later, we got the two Deadpool movies and the Deadpool cinematic universe. The character is a bit overrated anyway.
In terms of continuity, Emma Silverfox, Quicksilver and Banshee could be seen as an issue, but we can suppose that they are clones created by Essex Corp/WideAwake.
So my wild guess is that Emma Silverfox is Emma Frost's clone created by William Stryker Jr. in the sixties (DOFP established that Emma Frost was captured and killed) and later adopted by Mr. Silverfox, Kayla's father. Adoptive sibling.
The teen versions of Quicksilver and Banshee are clones too, of course. The real Banshee (First Class) was killed by Stryker in the sixties, while the real Quicksilver (DOFP) could have been killed by Team X down the line too, and that would explain why 2023 Wolverine knew about him and knew about his home address.
Thus, basically, we can imagine that Xavier recruited Emma Silverfox, Quicksilver II and Banshee II as X-Men, and they belonged to the second generation (along with Beast), operating many years before the first movie. Beast, Emma, Quicksilver and Banshee departed some time before, leaving Cyclops, Storm and Jean alone.
I don't think that they are "mutants with similar powers". Ironically speaking, and that's truly cool if you ask me, Stryker's secret files in X2 list two "Cassidys" and two "Maximoffs", without specifically mentioning their birthnames. Retroactive continuity, we can assume that the computer files referred to the clones.
The movie is set in 1983. 15 years before "X-Men" (1999). Cyclops is 18 years old, exactly like he was in "X-Men: Apocalypse".