Later, you plan to subdivide and build townhouses – all jointly owned.
However, if you fall off your motorbike at high speed, the properties pass to the surviving joint owner, regardless of what your Will says, unless you own them jointly as “tenants in common”, in which case you can state in your Will whether your half is to go to your son or his children.
If you wanted the townhouses to go to grandchildren, you would need to own them and then bequeath them via your Will, which I suspect would not make your son too happy.
CGT is payable when a property is transferred, except in the…