How many cresties can be kept together?

Hi i am quite new to the whole reptile keeping i brought myself and my patrner 2 crested geckos we are yet to know there sex they are about 3m old ish and we would like to get antoher two to go in the same tank as our first two. i was wondering as i have had them for two months can i add to them?
do males or females fight if more than one of each etc
pls help really want to expand them.

thanks Amy.

males will fight females can pick fights I think