No, that's completely wrong, partially because you are still assuming, when you say "add back in the 1/2 of 2/9", that they are selling 1/2 of the entire property. They can't do that- they cannot sell what they don't own! Each person can only sell half of what he/she owns. The first person owns 1/3 of 7/9 or 7/27 of the entire property. The second and third persons own 2/9 of 7/9 or 14/81 of the entire property. The sell 1/2 of what each owns that leaves each with 7/54, 7/81, 7/81 of the entire property. And, of course, together they still own 7/9 divided by 2= 7/18 of the entire property.