Yes, rabbits do it doggy-style, like most animals. I conjure up a picture of the pair crawling under the straw and havin' a cuddle while they do it face to face.
At 7 weeks it is not easy to see, but if you pick up the one that you think is the buck and shake it a bit, you should hear it rattle if it is.
"worst case scenario"???? If one IS pregnant you wait until they have kits and at 4-5 weeks make some of the children in your neighbourhood happy. (don't ask their parents first)
Seriously..... even with 2 females (does), one becomes dominant and may mount the other as a dominant behaviour. This happens with a lot of animals.
If you want to be sure and don't know anyone, find out where the nearest rabbit club is through the library. Or take them to the vet, they shouldn't charge a lot for determining the sex of rabbits (ask first).