Help required - power of attorney (building joint venture)

Dear Sir(s) / Madam(s),

My name is Ramesh. I require your kind help.
 

My brother and I inherited a property from my mother (mother died in 2010) and we have a legal heir certificate. We have a property of Sq ft 3500 and we had approached a builder for a joint venture. The agreement was 67% to us and 33% to the builder.
 

The builder has been good to us so far but we as owners have committed a mistake unknowingly. The builder had got an approval for four houses. We had given a power of attorney to sell UDS worth of 2 houses to the builder. For the first house the builder has the entire UDS and its part of his eligibility. However for the second house our UDS share also is present. Unfortunately we have given POA for UDS for both houses. This has been registered in the sub registrar office. As per the agreement the builder will sell two houses and compensate us through cash the extra square feet.
 

So as per the registered POA we understand that builder has right to sell the two flats covering the UDS without our intervention. Our main concern is that the builder can sell the flat to the buyer with a higher rate per square feet and compensate us with less rate per square feet.

 

I would like to understand how to deal with this situation and require your guidance on how to make sure we know exactly the price per square feet the builder has sold for. We are at this moment worried whether the builder will cheat us in selling the house to a higher rate per sq ft and compensate us with lower rate per sq ft.