Try to see if they are pooping/peeing in a specific place and put the litter box there. I noticed mine were going in a specific corner most of the time so I put their box in that area and whenever they went outside of it, I would put their poops into the box and eventually they started to catch...
One of my rabbits I have had for three years and for the lat year and a half it seems like she is constantly molting. Her coat is never clean and smooth and she always has some clumps near her rear end (sometimes it is worse than others). I try to help her out and brush/pet her till they fall...