It's sometimes hard to get inside a cat's head to work out what's troubling them, but something obviously is. Until you can work out what's upset them, I would suggest you keep them out of your bedroom so that they get back into the habit of using their litter tray again. Make sure you keep the tray clean at all times, and get a second tray, as some cats don't like using a soiled tray.
Are they indoor only, or have they started going outside yet? If the latter, then it may be that something outside has upset them and they'e soiling inside as a result.
Are they neutered/spayed yet? If not, please get them done, to prevent yet another litter of unwanted kittens to home, and for a whole host of other reasons. If they've not been done, they will be getting hormonal at this age, and this may be contributing to their behaviour.
Have a look at the link below and see if it offers any other suggestions as to how to deal with this.
http://www.catchat.org/urination.html" onclick="window.open(this.href);return false;