It might help if you clean the tank and all of the cage decorations (and hideboxes) then rearrange everything and place the geckos together. That way you reduce the territorial 'claim' of the first gecko. They will probably still fight a little. Or at least walk around stiff legged and wave their tails in the air but they should eventually work it out and accept each others presence. I often do this when I put breeding pairs together as well.
I have had a few females that refuse to accept the company of other geckos of either sex, but that is very rare.

Good luck,
John