it is impossible except for when you have cheats in Pokemon pearl,platinum,diamond
You can't breed legendary Pokemon eggs on Pokemon SoulSilver or on any Pokemon game.
No the only exeption is spiritomb only it can lay eggs
Legendary Pokemon do not breed, so they cannot lay eggs. However, only one legendary can breed, which is Manaphy. If you breed it with a Ditto, you will get the uncommon Pokemon which is Phione.
Latios
Deoxys cannot lay eggs, it is a legendary, no legendaries can lay eggs unless of course it was a cheat.
Well, I guess you mean "Soul Silver", and the main legendary Pokemon is Lugia, Water/Flying-Type.
the only legendary that you can breed is manaphy. and that will result in a phione.
Moltas: the fire legendary bird Pokemon the second strongest bird Pokemon
over 9000
They will simply gain Exp. You can't breed legendary pokemon.
no
It might depend on the Pokemon, though usually you can face legendary Pokemon again if you beat the Champion.