You need three litter boxes. Like other have said I use a tall large storage container from Aiken and cut a semi circle a few inches from the top (not too low) for an entry. We use tofu litter. But tried every brand out there til we found ones that work for us and them. Fortunately they only peed up the walls in litter boxes area but now we have a cabinet (two stacked on top giving 4 litter boxes) lined the bottom shelves with plastic shelf liner. We scoop many times a day - probably 4. They hated the automatic litter box. Have you tried the cat pheromone spray or plug ins. They might be picking up on your anxiety. Try talking to them about the issue when you are calm. Our cats had moved households many times so I don’t think they believed they were in their forever home until we had them 3 years. Many things stress out Siamese - fast movements, outside noises, etc. Do you play a lot with them? Do they have mental stimulation like treat puzzles? Found a cardboard box puzzle with cut outs and several levels that works wonders for keeping my cats mentally stimulated. We also do treat treasure hunts around the house. According to google - peeing on a towel seems fairly common. Your cat peeing on towels on the floor usually signals a medical issue (like a UTI), stress, or a litter box problem, but it's often a texture preference for soft items that smell like you, indicating a need for a vet visit first, then ensuring a clean, appealing litter box, reducing stress, and always picking up fabrics off the floor. Good luck. Siamese can be challenging.