I would like to purchase my parents' home, but it is during the 5-year look-back. How is the fair market value of the home determined?

My parents and all grown children live in ND. My parents moved into assisted living Oct. 2016. Dad just got transferred to nursing home status in April. I'm interested in purchasing the home my dad helped to build -- the home I grew up in, and that my parents lived in for 62 years until leaving it in October. I'm told family members have to purchase at full market value, while a stranger could buy it at 75% market value. (So unfair!!! This angers me so much, but that's a topic for another day!) I still may pursue the purchase, but the home needs a LOT of fixing up and updating. My question is how is "fair market value" determined? Is it through the free "market analysis" service realtors offer? If so, do I have to get more than one opinion and take the average? OR, do I need to hire an appraiser to do an "official appraisal?" If I do this, will this appraisal be valid for the bank financing my loan? I left a message with our elder-care attorney's contact person, but haven't heard back. I'm anxious to understand this piece so thought I'd throw it out here. Any advice?