I dont know what to suggest, do you have a local handyman who could knock something up for you ?
I dont envy you at all, Teabag is a sprayer, we call him Teabag Weebag or Norris McSquirter most of the time, he has calmed down a lot recently, but he is not allowed upstairs anymore and I am sure he knows why.
Will they not use a covered litter tray ? as for tracking, I know a lot of people on here dont rate it, but Biocatolet or Yesterdays News litter doesnt track at all, as you probably know from previous threads I am a bit of a OCD cleaner and could never use a grit litter as I woudl be hoovering all day and night, you should try Biocatolet, it may work for you and give you a bit of a break xxx