I would reccomend looking up the minimum requirements and showing it to your parents and talking about a solution to them as they can’t be on the patio in the winter or harsh summer temperatures. This step may help them see how serious you are and help them to understand how serious the situation is.
(Also if you were to neuter him his litter box training would probably go better as does it help to keep cancer risks down)
And idk where you keep the hay but having it IN the litter box or in a hay rack above it helps to encourage them to use it.
Back to things to do. Idk about your situation but is it possible to do some serious bunny proofing on your room and keep him in there? Then he could free range the whole room and only be in the cage when you sleep/weren’t home?
Talk to your parents about the x pen again and explain to them that you will put down blankets to keep pee/poo from going on the carpet/wood and that at the end of each day you will clean up any mess that he has caused until you can get him litter trained. This should keep it from attracting anything as my rabbit is free range around the room from over 16 hours a day and he’s never attracted anything.
You may also show them this article:
http://www.rspca.org.uk/ImageLocator/LocateAsset?asset=document&assetId=1232725725160&mode=prd
It will show why the RSPCA has made minimum cage requirements what they are (RSPCA: “royal society for the prevention of animal cruelty”)
Feel free to message me with any more questions as I’d be glad to help however I can!!