CGT tax on transfer on ultimate sale of land

The house and land were purchased two years ago and is owned 100% by the client's son. The first point is if the grounds do not exceed half a hectare, is a sale to anyone (including my client) exempt under PPR? I believe it is.

I believe it is legitimate to sell two thirds of the plot to my client and wife. Building work is then likely to commence and at some (possibly intermediate) stage the plot will be sold to a third party. Thus three CGT exemptions can be utilised in the tax year of the sale.

I believe the gain for each parent will be share of sale price less share of enhancement/building expenditure less value of purchase from son.

Is this feasible does anyone think? Anything, in others' experience that I should be wary of?

Many thanks
Peter
Peter Coekin