Hay in a big pile is the best thing for them. Hay is never wasted, you will throw it away but when they’ve had access to a big pile that they have played in, run through, snuggled into and most importantly been able to forage freely through then that has provided them with a great source of enrichment. Hay is so much more than just food for them!
You won’t be able to use just puppy pads because they will probably try to eat them. The puppy pads would need to be covered with something so they cannot get access to them. Typically if you use puppy pads, you’d lay a fleece over them so it wicks through the fleece onto the pads. A
A disposable bedding would be something like shavings, aubiose, paper bedding topped with hay.
It was just a suggestion, you may be able to find out what is going wrong with the fleece without having to use a disposable bedding. I was just thinking that you don’t want the piggies exposed to damp bedding.