In that case, the fair thing to do would be to get an estimate of the value of the property with and without the courtyard and divide the difference according to the unit entitlements and give the remaining owner that (and a bit extra to be on the safe side).
That way, if the fifth owner comes here for advice, I can tell them, hand on heart, that you have done the right thing and there’s probably no point in taking this to NCAT.