I hate to tell you, but it's going to be less effort to raise a competetive team from scratch. EV training is done by battling very certain pokemon- battling anything and everything distributes the EVs badly and to places they are not needed. The only way to save these pokes is to EV wipe via the use of -EV berries, and you will need hundreds to wipe an entire team. Read through the sticky in this forum call Compiled 4th Gen Guides, it details how EVing and IVing is done, the art of team and move composition, and is generally a very helpful thread. Sorry, but you're in for a lot of work to get into competetive battling