Okay give me some advice/tell me what to do..

I have a 20 gallon glass tank. aspen bedding, two hides, a basking rock and a nice size water bowl. So far I have three hatchlings in there, a female mojave, female pastel and a male cinnamon.

1st question.... My cinny and pastel cuddle, they are always wrapped up with each other or stacked ontop of each other in one or the other of the hides. My mojave on the other hand doesn't even like going in the hide, she sleeps randomly on the side of the tank or wrapped around the gages on the side. Why won't she hang out with her new friends? Is it normal for her to not even want to go inside the hides? and sleep just out in the open? Could she just be a loner and not want to hang out with the other two?? They are all basically the same age give a week or two.

2nd question.... My fiance wants 3-4 more hatchlings... same age as the three I have already. Can I put all 6-7 in the same 20 gallon tank, just for now while they are little then get a bigger tank a little later? OR will that stress them out having so many in that tank together?

any and all advice is greatly appreciated!!!
Thanks!