Please help!!! Cat's started peeing on bed after one night of being without litterbox

Ugh.  I got 2 SPCA cats 3 months ago.  Perfectly litter trained, no issues whatsoever.  3 days ago I woke up to a sofabed covered in pee and poo (same room where my son plays and also where their food and water is).  My husband had cleaned the litter box the night before and accidentally left it outside all night so poor cats had no access to it!  We washed blankets immediately but next morning it had been peed on again.  So I closed the door to that room and moved their food/water to another spot. This evening I was putting my son to bed and called the cat in for his usual cuddle---he came in and peed right on the bed beside us!    I'm assuming this must be because he was without his litter box one night but what do I do about it now???  It's costing a fortune in laundromats and rug cleaners and it's only been 3 days.  Not to mention I don't want cat pee all over my house!     Anyone know what I can do at this point?  Thanks for any suggestions....

Are both cats peeing outside the box or just one of them?  

you need more than one litterbox -- preferably 3 but at least 2

Oy; that is really frustrating! 

Be sure you are using a good enzyme cleaner.  If they can smell it; it may draw them back. They can smell what we cannot.  I have used Nature's Miracle; but there are others.  You really have to saturate where the urine went for them to work and it can take more than one cleaning at times too.  

It's also a good idea to consult with your vet to be sure there are no health issues going on; such as a UTI.  The fact that he peed on the bed right in front of you makes me more inclined to be concerned that could be going on.  

I do agree that it would be a good idea to add a litter box or two if you have the space.  Some cats develop a preference for using one box to urinate and the other to defecate.  

Good luck!!