Hey big leb, nice problem your friends have, and great to have six kids to share it amongst.
This is a common problem in farming families, complicated by sentiment and business opportunity.
Wills are always messy, best to sort as much out as possible before hand, as amongst six kids their circumstances will change in ways impossible to predict in even a few years' time.
If I was your friend(s), I would sell the four blocks as soon as possible, and average the gift amongst the five kids who don't want to build there. The child who wants to build there should receive the 5th block, but make up the difference to the others (receiving one block out of five, to restore the value to one sixth).
The house block your friends should keep, not knowing the health bills they will face in the future and borrowings they might need to make, and one or both of them may need to sell it to move into some form of aged care down the track. The expectation of the kids should be that they have received their inheritence, and are in the fortunate position of being able to say thanks.
In the will, therefore, they only need the normal request for the excutor to realise the value of all assets remaining after debts are settled, and that this amount, if any, be split six ways.
And property and money are incidental to family relationships anyway, particularly in big families.
