From the IRS at:
https://www.irs.gov/uac/IRS-Issues-Home-Sale-Exclusion-Rules
"For joint owners who are not married, up to $250,000 of gain is tax-free for each qualifying owner."
And from nolo.com at:
http://www.nolo.com/legal-encyclopedia/how-does-the-capital-gains-tax-exclusion-apply-three-co-owner...
"As long as each unmarried co-owner satisfies the two-out-of-five-year ownership and use tests, each gets to exclude up to $250,000 of his or her share of the gain from the sale. (Married couples who file jointly can exclude up to $500,000 of their gain)."
