People say 10gallon is good for ONE gecko, but I personally don't go anything lower then 15 gallon per gecko, but it's better to house them individual anyways ..
some say that theyve had success housing multiple females together year round, but i've never had any luck with that. i house all my gecko singly because when they were together they would bite/bully/chase each other.
okay this is a really interesting topic I just got two that have been together for a couple years in a 10 gal. once I had them I moved them to a 40 and they have never had a problem with getting along. no bite marks or anything like that. in fact when one is out of the tank being held the other is watching it through the glass. like it misses its buddy. My nephew want to put another one in with them but I wasn't sure about it so I was asking about that on another thread.
I have several tanks that house colonies of females, but they are large tanks and the females have set out their own hierarchy. I have plenty of hides and multiple feeding dishes. In a 29g I would do 2 females, but be prepared to separate them if they don't get along.