tank size for my juvenile and NEW BABY gecko

so today i just bought a new crested gecko that i have been looking at for a few days now and i couldn't resist buying him. but i put him in my zoo med 12x12x18 with my other two geckos Booger and Mocha who are a few months older than him.

my question is, should i keep him in there for a little bit so i can get some more money to buy a new cage for him or should i take him out and put him in a krater keeper for now? i only plan on him being in there for maybe 2 weeks max before i can buy or build him his own terrarium. i have TONS of cover for them in there so they probably won't see each other much.

I'm sure its fine but i just want to make sure. i don't want my crested gecko tank to be too crowed.

or another question, can i keep the 3 of them in there until they get bigger and then upgrade the tank size?

any help?

how big are they all?
pics?
if they are still relatively small they should be ok together, as long as they cant fit the younger one in their mouths.