Not Celadon, that's for certain. If you're going to flee, for a while, it's best to avoid staying near the trains once you pass over to the region.

[He sighs softly. He doesn't remember much of it either, but he did do a bit of research.]

If none of you have a pokémon who knows Fly, then... you may want to acquire a bicycle. It'll make travel a bit faster, if you think you're able.