I am sorry to hear you are having issues with your darling cats urinating inappropriately.
Unfortunately, there are many reasons for cats to urinate in unusual places. It can be due to disease processes causing excessive urination (eg. kidney disease or diabetes), inflammation of the lower urinary tract (eg. idiopathic or infectious cystitis, bladder stones), or neurological issues. It is also possible that the inappropriate urination may be due to marking territory.
To get to the bottom of why this is happening, and to find a solution, I suggest heading to your local vet for a more detailed conversation and thorough examination. Ideally you would need to find out which of your cats is urinating on the bedding. If unsure, it would be best to take them both for an examination. Your vet will most likely want to get a urine sample in order to run some tests, and potentially further diagnostics following this.
I hope together with your vet you can get to the bottom of why this is occurring and find a solution. It is certainly no fun to have your little munchkins urinating on the bed…