You can sex 'em at that size, it just may be a little hard to see lol. But you definitely can, I sex them around .5" so I can start selling them, you know, when I have broods lol.
I'm going to get my super magnifier out and see if I can sex them. I'm almost afraid to pick them up they're so tiny.
Keep an eye on them, they may get along with each other. Otherwise, they'll let you know when they no longer "enjoy" each other's company (once you have them sexed you'll have a better idea, too ... M:M is going to be bad, M:F will be alright, and F:F will be alright). But that aside, once they hit sexual maturity I'd consider separating them, which I believe should be the 3-3.5" mark for them, just because this species has a reputation for being anti-social and aggressive (but so adorable lol).
If they'll get along I'll put them in a 30 g, whatever they want. It'd be a lot easier than having to seperate. They (the Blues) don't seem to be moving around much or eating anything. The little white one's already got a heck of a personality. I've got silk & plastic plants that go up to the top of the water level (tank is sealed 100%) and she acts like a monkey crawling all over them all over the place. If her little claws were bigger she'd let me hand her an algae tab chunck. She just sits there and I put it in front of her and she snatches it up. She's not even scared of me 
