What do I keep missing?

[Petzbreeder]

When I arrive at Lilycove City, the Wailmer/Wailord blocking the way to Mossdeep City are always there. I can't work out what I keep missing in the storyline to get rid of them. Unless it is possible to bypass them by riding Latios/Latias, I haven't got a clue as to what I keep missing in order to get there.

To be honest, I could never work out how to get past them in the original Ruby/Sapphire either!

[the bread dragon]

go to slateport city and talk to catpain stern, then go back to lilycove and go through the magma/aqua base

[Jacquelyz]

I'm going to use this forum because of the content I'm interested in.