Running Two Serial Cracked Games on LAN.. Is it legal?

[Coldkilla]

I have two copies of Rome Total War & ever since I've lost all my serial keys for all of my games.. i was wondering if this is possible:

1. To find two cracked serials and have them work together (I tried this and it didnt work, I was wondering if there was a way to)
2. Is it legal?
3. If it is legal, how would I go about doing this? For the game to work online is not that important, i just want to play against my little bro in a game of one on one
4. if it isnt legal.. ppplease tell me, so i can see if I can purchase new keys from the company.. or even if they do that.. otherwise i'll have to repurchase both copies of the game