Peeing is often a way to mark territory...especially in unfixed males. Since they started and then stoppen once, it probably is the sex-drive giving them the urge to let the world know they are ready and willing.

As everyone else said, at least two boxes and a trip to the vet are in order. Another thing that might be happening is another animal may be visible through the windows and they are marking to define their turf. (Neutering will lessen or end this urge)

Please give them the chance to be fixed before you decide to not keep them. There is a great product available at Wal-mart or Sam's Club called oda-ban that does a good job on the places marked.

You might try keeping them in one room with two litter boxes until they have their appointment. It will at least contain the problem. Of course let them out to play when you are home. Since the spots they go seem to be in obvious places, it sounds like they are trying to tell you (or the world) something, not being "naughty" Once you figure out what is wrong, the problem will end.

House cats set outside face a very hard time. I've rescued many and buried others. They don't know how to hunt (which is a learned skill) or how to avoid dangers. If you do decide not to keep them, please try to find a no-kill shelter or foster-home. You obviously care about them or you would not be posting here... once fixed I bet you will find you have solved the problem and have years of joy with them.

good luck!