Litter training a pair of bonded buns..Help,Im stuck!!!

BB is neutered.He is 2 in a few weeks and lives with his sister,Lily Shane.
Both bunnies have spinal problems but no mobility problems to match.
Currently moving buns into new set up.Have tried a few but not much luck.
Am now trying shower curtains and puppy pads.:roll: I do find urine in the tray...dont know who does it though!!!
Poops absolutely EVERYWHERE!!!
Hay is in the litter tray...and I do put poops in the tray to encourage them to go in...
The thing is,Im now trying a carry box as Lily cant jump over the cage bottom like BB can, so its a whole new "Living space" with a carry box filled with hay, a couple of tunnels and a litter tray and like I said, shower curtains and puppy pads.So frustrated.My outdoor buns are wonderful!!!
Any input gratefully recieved.xxxx
BTW,Lils isnt neutered.She has lots of problems and is best left unneuterd at vets advice.

Anybun???

if the enviroment is changed lots then they will likely be marking their territory also if other buns are near by this can make them do it more, how about a storage box lid with newspaper and hay on top as a litter tray ? i find with my bun with leg issues this works rather well, her not being nuetered sadly (while obviously nessacery due to health reasons) is likely making it less easy to litter train as she will feel more territorial, keep scooping all the poops up and putting them in the tray every day until they (hopefully) get it xx