Okay, then your 3 month old of unknown gender should not be housed with those other two.
1) The huge age and size disparity could easily result in dominance/bullying, which could get very serious and lead to lack of food, injuries, or even death of your little one.
2) All new geckos should be kept away from all other geckos for a minimum of 60 days. If you were unlucky enough to buy a leo with something like crypto and then put it right in with the others, it could kill all of them. The sooner you separate them, the better chance you have of them not catching anything your new gecko might have.
3) 30 gallons isn't big enough for three leos. Two? Sure. But three shouldn't be in less than a 40 gallon. (Rule of thumb is 20 long for one leo and 10 gallons added per leo. So a 20 long for one leo, a 30 gallon for 2 leos, a 40 gallon for 3 leos, etc.)
~Maggot