I am so sorry! I completely understand your frustration! I have a similar problem right now with Allen and Pouncer peeing, though I know exactly why --- their room has been closed off and Minette now has it. They are very peeved kitties.

Is it possible your cats are also peeved? Maybe they feel their territory has been changed to make room for baby? Have you recently begun to paint and move things into the nursery? Did they hang out in that room before and now are shooed away from it?

It could be that the boys were mad first, peed on Samantha's bed. the girls came along, smelled it, then they peed to cover the boys' scent. It could be a multitude of things!