Unused uds

Hello, Explaining my scenario for gaining clarity on unused/unclaimed UDS. A piece of land measuring 3802 sqft had 8 appartments that were constructed but each one was provided a UDS of 1/12 which comes to 316.8 sqft each and this is mentioned on each of the sale deeds. The builder owned one of the houses and the original plan was to construct 12 houses but the remaining 4 were never constructed. Now the entire appartment has to be reconstructed and the original builder has sold his house to the new developer who is entering this purely as a contractor and not as a joint development. The new builder has since bought another house among the 8 as well, now owning 2 out of the 8 houses and the UDS they own should be 2/12 shares. The remaining 4 UDS is not registered when the old builder's house was sold to the new builder and the other owners are not sure of the unclaimed UDS. Now the new builder says that he has access to the other 4 UDS as well since the old builder has sold it to him along with the house and now he owns half of the land. My questions, 1. Is it legal that the unused UDS can be sold to a third party without informing the other owners? 2. If it is not legal, can the 1/12 UDS be converted to 1/8?