The deed (public record) for the farm shows a purchase in 1998 by someone named John Lundberg. Then in late 1999 it is amended to say John and Bonnie Lundberg. At that same time in 1999 the property is transferred into an LLC, Sweet Grass Farm". The mailing address for the LLC on the deed is the same as the Lundberg home address. Minimal googling does not indicate that these people had any “horse involvement”.
So one would presume that at the very least this couple is the primary owner or owners, though it is entirely possible that someone else (MB) could be included as an owner. It is also sensible to assume that if one was going to lease their property to another party that movement to the LLC would be logical in order to protect their personal assets in case of a problem.
Another edit: The docs in NJ also show that Sweet Grass Farm assigns to the bank holding the mortgage all lease and rent payments.
Edited to add: property search in Florida does indicate MB as the owner of that farm which was purchased by him in early 1999