Parents selling house under LLC to child strategies?

[Trevor Mork]

My wife's parents have a house that we are renting that they wish to sell to us. The house is currently owned loan free under a sole  proprietorship llc. What options might there be to help them/us pay as little in taxes and transfer costs? We would need to borrow aprox $140- 200k to purchase after putting 20-40% down. Her parents have not lived in it for the 2 of 5 years to deduct capital gains.  

Just looking for the option that might cost the least to transfer.

Options as I see them (Traditional purchase with mortgage, Owner finance, Purchase the LLC from them leave deed in llc name) Any advice would be appreciated.