Firstly, welcome to the forum!!
Have you checked the gender of the mouse that didn't give birth? It's possible that you have two females but one got pregnant at the store. If the other one is indeed male you need to separate them NOW otherwise you'll have another litter in a few weeks (and she could even be pregnant again now!).
I would leave them alone for another day or two before you move them (carefully). At this age you should be able to see pigment in their skin and can handle them a bit. Handling them at a young age is very helpful for later.
The mother should wean them when they are 21-26 days old. At this age it's important you separate the male babies since they can mature that early! The girls can be left with mom for longer or even permanently, should you decide to keep them.
I would start posting ads on craigslist and asking around in pet communities to find homes for the mice. Having a small
adoption fee will help ensure that they go to a decent home and be sure to specify that they are for PETS only. Otherwise they'll probably end up in a snake's mouth or a laboratory. Mice can be hard to rehome so be prepared to at least keep them all temporarily.
The females could all be kept together in one cage. Male
litter mates can get along but in most cases will end up fighting as adults. Males are usually best kept singly.
Good luck and keep us updated!!
)
