Establishing cost-basis for inherited property split between siblings, and then years later buyout of 1 sibling.

Property inherited in 2001 by 3 siblings, FMV was $112,000.  In 2012, 1 sibling wanted out.  Other two siblings bought out.  FMV at that time was $100,000.  Property sold in 2020 for 200,000.  How to split out the cost basis?