Pull the F26E fuse.
When your three is at the normal height and all seems OK, shut the engine down, open the bonnet, and remove the cover to the engine compartment fuse box. Remove 20 amp fuse 26 and then put the fuse box cover back on and close the bonnet and start the engine again.
A few red lights etc will come on, but the suspension system is now disconnected; air compressor will not operate, vehicle will not raise or lower, but it will drive normally etc. It is just like you did not have an air system but had metal coil springs.
Now drive around for a few days and if you do not have the parking brake problem, then the problem is air suspension related. This I would regard as good news as then that helps to isolate the problem.
If you still have the parking brake problem, then I think probably there is a broken conductor somewhere and that is somewhat difficult to find, but not impossible.
Start with removing the F26 fuse and see what happens, or not.
The link below is to F26 related information as well as other fuses related to the air suspension system.
https://www.disco3.co.uk/gallery/thumbnails.php?album=3778