They all came from the North Crater but Rheas idea of them being created and based on diffrent geological regions is very valid indeed. The Planet could have created each WEAPON to fight in a diffrent terrain, to search for Jenova easier (Fighting back against Jenova being their original purpose).
Ultima WEAPON = Air-born for aerial fights and such.
Diamond WEAPON = Ground coverage
Emerald WEAPON = Underwater
Ruby WEAPON = Sand and other lose terrain
Jade WEAPON = Not a fucking clue
Omega WEAPON = Doesnt matter, everythings dead when its supposed to appear anyways
Chaos WEAPON = Doesn't matter, your all screwed
Chaos wasn't a weapon, i don't think it was at least and Jade was the airship thingy, that looked like a stealth fighter