Your father needs to file a chapter 7 bankruptcy. IF he does not and just lets the old non paid loans stay out there they can come back in the years to come and make him pay them. The bank more than likely has a second mortgage on all of his property. Most banks have a uniform lean on all equipment and real property.
Like some other have stated. Get the tractor on your property. On the so called friends it can be pickup at anytime without any warning. At least if it is on yours they have to give you notice. Now that notice can be a truck with a sheriff deputy to pick it up. So you need to be able to move fast if that happens.
You would need to know what the original loan papers stated the banks held as collateral. Also if your Dad later signed any changes to the original papers.
I then would go to that bank if they seem to have a lien on the tractor. Have an appraised value on the tractor in its current condition. I would pay a reputable local dealer to write one up for you. I would also take some pictures with you. When they see that it is non running they should jump at a chance to get a reasonable salvage out of it without any recovery cost. Now do not get stupid and offer them a super low amount. Like $200 dollars or some thing. That could mess the deal up. They then could round it all of and sell it in anyway they want.
BE straight and honest and they should be relatively easy to work with. Try to get cute and they can bury you with much better lawyers that are used to collection these kind of debts.
Some of the subjections on here have been laughable. PLAY IT STRAIGHT and things usually work better.