Granny flat options - Parents need somewhere to live

Hi all,

Construction is just starting on our forever home on our 3328m2 sloping land in Sunshine Coast. Coincidentally my parents rental lease is not being renewed and they'll need to find somewhere else to rent within a couple of months. With the cost of renting continuing to go up (along with everything else), we're happy to have them live on the land, and had considered something in a couple of years, but their imminent eviction has got us thinking about bringing this forward. Is there realistically anything we could do with our land in the next few months to provide them with accommodation (medium to long term)?

The site is sloping (1:6 to 1:3 in parts), so it isn't quite as easy as on a flat block.

Some options we've considered:
1) Buy a caravan, but not sure how we'd do septic / water / electricity. Cost wouldn't be a problem, and land is large enough that it wouldn't interfere with our build.
2) Build a class 1a shed. Not sure how long it would take to get it built, perhaps 3-6 months? Would need to get it wired / plumbed up to the house.
3) Any type of proper granny flat would likely be 8-10 months, and probably wouldn't be able to get it mortgaged until after our house was complete and re-valued.
4) Kit home??

Let me know what you think.