IF you are playing separate worlds it doesn't matter. Like Jake said.
HOWEVER if you wish to play in the same world things get a bit trickier. First you should let the admin know BEFORE the 2nd player makes their colony. So you don't get banned before the admin gets to their messages. Secondly while it's not recommended that you play in the same alliance or even the same world. I have been allowed to play along side my younger brother on several occasions, in the same alliance. But you will first have to PROVE that you are two different people to the admin (usually not brand new, active, Facebook accounts are enough), and your log on's and such will be monitored extremely closely (as well they should). In truth I think it would be a larger advantage if someone in your household was part of another alliance. At least together you're pooling from the same resources, same area, share the same radars, same gates, and same allys and teammates. With someone in another alliance it would enable you to do far greater and influential things in my opinion.
In the same household and alliance the biggest thing you could do is notify the other person A common thing in top alliances although we use a text or phone call as opposed to yelling up a flight of stairs. Or even say you were to commit the LARGEST BD offense out there and log on to their account (since you may know their password). In truth that's not much different than what may alliances do and share info *Just In Case*. Personally I don't think either is fair or right and I don't allow either, but I realize the latter is far more common than most people are willing to admit.