Only if he waits two years after the date they gift their 2/3 portion to him. 

The way it works is when there are joint owners, each owner can qualify to exclude $250,000 from their portion of the gains on sale if they meet all the qualifications.  So as it is, he would qualify to deduct $250k from his gains, but the parents would not.

They can't just gift their interest in the property to him and have him qualify right away to deduct the gains from the whole property, because that portion of the property wouldn't yet meet the 2 year requirement.