The question is can the second family use the installment method of reporting? if they can then they can report the sale in the year they receive the proceeds. however, the issue is one of constructive receipt. if the holder of the funds is a rep of the family or the family has control over the funds, then I would say they have constructive receipt on the date of closing - no installment sale. I can't say if it's possible to do two sales if the property is undivided, see a real estate lawyer
