If you only have 7 hens with one rooster, chances are very good that all of your eggs are fertile.
You can actually tell if they are fertile when you crack them. You can see a small bullseye on the yolk. Although sometimes it is underneath, and you have to flip the yolk to see it.
ummm if your asking about seperating them cause your worried about all the hen's eggs being fertile, you dont have to worry about it. 1 rooster can fertilize more hens than that i think the ratio is like 1 roo to 10 or 12 hens
If your chickens are mature, chances are your rooster is doing his job. I would crack a couple eggs and look for the bullseye on the yoke. If you are not sure what a fertile eggs looks like, do a search here on BYC. It is very easy to tell.
I guess I should add that you only need a breeding pen if you want purebred barred rocks, and can't tell the barred rock eggs from the other breeds. If that is the case, then yes, you should separate out the BR's, but all of them, not just one or 2.