Hi again, Samantha.
I was hoping to get some additional information from you, but I also didn't want you to wait too long for an answer.
Typically, when a cat starts weeing and pooping out of the litterbox, this can indicate an underlying medical problem, so my first suggestion to you, would be to have him evaluated in person by the vet and have a urinalysis and urine culture done, plus a fecal sample analyzed for hidden blood and/or intestinal parasites.
If there is nothing medically wrong (hopefully), then this has become a habit and it's very important that you clean the areas he has soiled, with an enzyme-based cleanser like Nature's Miracle, Zero Odor, Odor Mute, and many others, available in your pet supply stores. If you need to wash your linens, Nature's Miracle makes a laundry detergent and additive.
The products I mentioned are available in the U.S., but if they don't have them in your area, try to find something similar. the 'enzyme' action is what is most important to remove stain/odor so your cat won't return there to soil again.
Make sure you have more than one litterbox, and with 3 cats, you should have 4, if you have the room. The 'rule' is one box per cat, plus one. Keep the boxes clean at all times and add some 'Cat Attract' to their regular litter. This contains herbal attractants that encourage use of the litterbox. Also, use large, uncovered boxes.
Close doors, where you can, so he can't get to the places he's soiled in the past, and after he eats, place him in the litterbox and gently take his front paw and 'scratch' the litter with it to remind him what he has to do, there. If he jumps out, put him back in and repeat the scratching. If he jumps out again, leave him alone for 10 minutes, watch that he's not eliminating anywhere else, and then put him back in the litterbox and scratch with him. Cats usually eliminate (mainly urinate) soon after eating, so that's why I'm suggesting this.
Cats poop less often, but one of the times you put him in the box, he might do one or both.
I agree that the Feliway plug in pheromone diffuser is costly, but you can get just one to put in the room where he is soiling on the furniture and/or bed. It also comes in a spray, which you can use to spray in the corners of the rooms where he's soiling and don't allow him access to the room until the Feliway is completely dry (about 20-30 minutes). This will make him think he's already 'marked' there and he won't do it again.
Yes, this may be marking behavior, if you have any stray unneutered male cats (or any cats) who hang around your house. He may feel the need to mark, to defend his territory.
Even though he gets along well with his companions (siblings?), something may be stressing him and causing this behavior, so the last resort is a vet visit so he can be evaluated in person and perhaps in this case, he will need some prescription medication to help him stop this behavior. There is a variety of medications (anti-anxiety/anti-depressant) that are used in these cases, an discuss with your vet, a medication called Clomicalm. Here is more information:
Of course, again, you'll have to see what medications are available in your area.
One more tip: when you find a poop on a bed or furniture, take it and place it in the litterbox, then show it to him and have him smell it, so he associates the box with the poop.
I hope things will improve, soon and please let me know how things are going? Thanks!
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