Paralegals ethically cannot give legal advice, they cannot fill out paperwork for a client, and I'm pretty sure there are only a few matters where a para can represent a client in the court room.
It sounds like the unwilling relative has committed borderline conversion, and that should be reason enough to get the police involved.
As stated before, I'd get all of the documents rounded up, coggins and what not, and hire a horse hauler and what not. Get down there and claim your horse. The relative has no right to keep the horse against the owner's will, and thus could be charged with an array of different violations.