Here is a list of all the legendary and awesome Pokemon you can't catch in the wild:
raquaza- sky pillar (pre & post e4)
kyogre- see weather institute (post e4)
groudon- see weather institute (post e4)
latias/latios- on tv red=latias, blue = latios (post e4)
metagross- get egg from steven's house in mossdeep (post e4)
requires event/ procedure
regice,regirock, registeel- more info on Google
deoxys- special event
mew- special event
ho-oh- special event
lugia- special event
its not an emerald its RAYQUAZA the main legendary Pokemon in Pokemon emerald.
rayquaza
The three legendary Pokemon in Pokemon emerald is Kyorge, Groundon and Rayquazer.
Groudon, Kyogre, and Rayquaza. Groudon is the fire legendary pokemon, Kyogre is the water legendary pokemon, and Rayquaza is the air legendary pokemon.
Raquaza (sorry if I mispeled that)
Tornadus, Landorous, Reshiram, Virizion, Terrakion, Cobalion, Kyurem, and Victini.
There are no breedable legendary Pokemon in Emerald. In Diamond/Pearl/Platinum Manaphy is breedable with a Ditto. However, the offspring will be a Phione.
legendary Pokemon cant breed
all the legendaries and how to get them here http://www.psypokes.com/emerald/legendaries.php
Rayquaza is the mascot for Pokemon emerald which will be stronger than Groudon and Kyogre
yes
No legendary Pokemon cannot be bred