What are the tax implications of a sibling buyout…

Hello - Three siblings inherit the family home in Jan 2021: 1/3 Joe, 1/3 Peter and 1/3 Mary.  Now, Joe would like to gift his 1/3 share to Mary. Peter would like to gift 1/3 of his 1/3 share to Mary.  What is the best way to account for this and what are the tax implications?