Is this to say without franklin Richards? Or Phoenix? Or only mutants that could conceivably be convinced to help?
For my dollars it would all start with
Damian Trypp, Sr.
Who both knows magic, and can control time to a degree that he knows the moment the JLA attacks our earth.
THEN
Gabriel Shepherd
Matthew Malloy
Jamie Braddock
Legion
Nate Grey
Mister M
Vulcan
Just these guys alone would get it done.
Maybe any 3 of them plus Damian Trypp.