A lot of it has to do with the size of the snakes, whether they all eat the same size prey or not.
I try to feed on particular days but with my busy schedule it doesn't always work out. I also breed my own rodents so cost of throwing a few away isn't much of a factor for me.
I've got 2 adult burms which eat large rats and 6 other various snakes that eat sm - med rats. I've also got 5 baby burms that eat rat pinkies.
In general, I try to feed each group on different days, sometimes combining the adult burms & sm - med rat eaters. By not "feeding till they puke" (completely stuffed) I'm usually able to give an extra rat or two to some of the other snakes. This involves knowing their limit, which takes some trial & error in order to establish a baseline. (I don't mean to insult your intelligence/experience, by any means, just trying to make things clear, that's all.)
Your problem is you need a monitor and a gator to feed off leftovers to. Great garbage disposals, they are. Rarely refuse a meal, no matter how stuffed they are. Ha! Ha! For me, that's where any other leftovers go now. 
I have re-freezed rats thawed at room temperature a few times without any problems. I don't recommend doing it to one that's been heated thawed quickly in warm water, though. One problem with re-freezing, which can usually be done a few times per rodent, is each time it's thawed the membranes thin out & when their skin bursts, tears, it stinks to high Heaven and is plumb messy.
With seven snakes, you should know your snakes' limit to where at the most you'd have one, maybe two, leftovers at a time. If you continually have leftovers, don't completely thaw a few rodents until you see they're needed.
Have a good one!
HH
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Due to political correctness run amuck,
this ol' hillbilly is now referred to as an:
Appalachian American