I agree with the comment above, I've always housed my Cresties at 76, and I bump up only 2 degrees when breeding occurs (Which is also the same temperature I incubate at). Separate the pair for a week or two, then try again!
Hard to say at such a young stage, but I would chance saying female. As for what that is in the middle, good question! I've had it on several of my younger cresties, then it just up and disappeared! I've heard that it could be an indicator of gender, but in my experience the gender went both ways.
If they are both female, and you have the appropriate sized tank, absolutely you can house them together. However, if they are both male, DON'T DO IT. Males can be very territorial. Female and Male may be housed together, but I would wait until they are the appropriate weight, as the male will...
This is called "firing up", and there's a lot of debate of why Cresties do it. In my personal opinion, it's a comfort thing. All of my Cresties fire up at night just after they get a humidity bump, then go pale again during the day while they sleep!
In any case, its completely normal, and I see...
I would like to make a self-sustaining live plant vivarium with crested geckos, at my disposal I have the following:
Crested geckos (Any amount)
Glass front opening tank (36 tall, 24 wide, 18 deep - Equal to about 70 gallons)
Fog machines (Up to 4)
Lights (Any color or size)
Heating utilities...