Jack/Tubby,
My advice and my OPINION ONLY.... Take them all into the house and separate them by sex NOW! Keep the temperature at a constant 70-75 degrees. Feed them well with all the necessary "artificial" lights. Best thing is keep them in 2 very large tanks - let them see but not go near each other. In two weeks, release them together when the weather reports a string of several SUNNY days of temps at 70 or better. Release them early in the morning and let nature takes its course. I cannot guarantee sucess but after having at least 1 or 2 boxies for over 35 years and studying them, I found some tricks/tips that worked for me. (I've also adopted a few that people just couldn't care for them anymore) Let me say that there is something with natural sunlight/fresh air that really gets them going. BUT you have to do it when they just come out of hibernation. You can't wait for a couple of months - That just won't work then. In regards to size or area, the more the better. One male is all you need. However, I found that sometimes having more than one male is better. But if you have more than one male, you NEED ROOM. If not, you may regret having more than one male. The ideal ratio to me is 6:9 or 3:5.
By the way, I do NOT intentionally breed boxies, I find it more satisfying to find hatchlings walking about. I also do not sell boxies. I only adopt boxies and study them for personal fun... (boy, I gotta get a life). I could care less about colorful the shell is...etc. I have some with bad shells, even took in ones with swollen ears (now healed), and even cracked shells (old injuries) when they were hit by a car or chewed by another animal. But I can tell you that they are now all as healthy as they can be. The only boxies I refused are the ones with respiratory problems. (Can't afford to spread that around). Anyway, hope the above helps. Remember, It is MY OPINION only and nothing else. I'm not on the net that often but ask away if any questions. I can only tell you what worked for me. Anyway, you have a lot more qualified people on this board than me Harry.