What are EV's and how do they work?

EV stands for Effort Value, or something similar to that. EV's are the stats of IV's, and whenever you win a battle, your EV points go up some. When you finally reach a new level, it adds together all the EV's you obtained in the previous battles, and that determines how much your stats will increase when you level up. That's all I know about it at any rate, if you would like more information on EV, IV's and how they work, then look here.

Http://www.supercheats.com/nintendods/pokemonpearlwalkthroughs.htm

There should be a guide to EVs.

EVs are hidden stats that can increase the value your stats (Attack ,Defense, HP, Special Attack, Special Defense, and speed). When you defeat certain Pokemon you will gain a certain number of EP (Effort Points). 4 Effort Points make an Effort Value (EV) which will increase the stat you have the EV in. The is a maximum number of EVs you can have, but I do not know it.

I'm afraid I can't rate your team without seeing it...
But on to EVs. Ill try and say what the other guys missed, though they got most of the important things. The point about 4 EVs equalling one stat point is important. Pokemon will generally give your Pokemon EV points in the stat the Pokemon defeat is strongest in. For example I have my absol, I run around and beat 5 kricketune before going up another level. Each kricketune gives 2 EVs towards attack so 5x2=10 and therefore hit absols attack stat will go up 2 points extra then it would have if I had used a rare candy for instance. The other two EVs get carried over to the next level. There is a limit to EVs each Pokemon is allowed 510 total EVs with the max for one stat being 255 (though if you count make it 252). That corresponds to 64 extra points making EVs a fairly important thing to pay attention to when raising your pokemon.
Each time you defeat a Pokemon (outside of the battle tower or link battle) all Pokemon involved in defeating that Pokemon get the same number of EVs (ie 2 attack for the Kricketune. It may seem like a long excruciating process but it can be made easier by use of pokerus or the macho brace or both. Both of these allow your Pokemon to double the EVs they acquire in a battle. So if my absol from above was holding a macho brace he would get 20EVs instead so +5 to attack.
Pokerus is a rare thing that pretty much serves no purpose other then double EVs. If you are lucky enough to get it, take advantage of it. So say that same absol was not only holding the macho brace but had pokerus... He would get 40 EVs! Hurray!