Restraing order

We have an ancestoral house in Delhi & me , my mother & my 3 brothers are equal shareholders. We had entered into an agreement with a builder in which he will construct basement , ground floor & 3 floor's above. The builder will also give some consideration amount & retain basement & ground floor for which we have already entered into a sale agreement . The consideration amount was equally given to all five by the builder & we have transferred that amount to our mothers account . Apart from this amount the rest of the three brothers were supposed to give the balance amount for my & my mother's share. Now the problem is that the building is on the verge of completion but so far we have not received any money from them. My mother is staying with me & we live in another state , we are afraid that the brothers might take the possession of the three flats on completion without making the payment. How can we stop them from entering into the flats , Moreover we have not entered into any written family settlement agreement.