I'd go with a trimmed and tweaked version of the Giant Size X-men.
Xavier
Storm
Cyclops
Nightcrawler
Sunpyre
Siryn
Thunderbird
Xavier would be more in the background as a mentor figure, rather than the pov character he has been in recent years. He would be this series' Dumbledore so to speak; kindly but mysterious, with the film only hinting at his true power. I'd cast a black man as Xavier, it just fits so well. In 2018 the Martin Luther King allegory should not be a white man. With that one racebend the team has a majority poc cast.
Storm would be a pre-established character from the Black Panther movies. For years she has been living as a demigod in the deepest parts of Wakanda, but as more and more mutants are activating around the globe she decides to take an active role in mutant affairs and teams up with Xavier to establish his school for gifted youngsters. Never his deputy, she would be an equal to him in her own way, as mysterious and awe-inspiring to Xavier as to the students, but still with a warmth to her.
Then we come to the young students, all within the 16-21 age range. Storm and Xavier would be more in the background, but these guys would all share roughly equal screen time.
Cyclops would come into his own as the X-men's young leader. Nightcrawler as the smart guy/the comic relief, but beneath that he is the one with the most obvious mutation, so there's a good hook for his character arc there. Thunderbird as the loner who eventually warms to the rest of the team. Instead of Banshee and Sunfire, I've decided to go with their female counterparts for some gender diversity. Siryn would be our teams "heart", Sunpyre would be the arrogant, jerk with a heart of gold co-leader.
As for Wolverine and Colossus, I felt like the team was big enough at seven and these two were the clear candidates to cut. Wolverine is overexposed, and if Deadpool is retconned into the MCU, Colossus could follow, so no need to recast him.