Cost to bring Stay Order

My late grandfather has writen a registered WILL(in 1995) on his house, giving life-time interest to his son (who is my father) and the absolute ownership to me (25% share of the house property), my brother (50%) and to my step-sister (25%) which is applicable after my father passes. My grandfather has also written a condocil which states that my father can make property improvements (bank loan limiting to 15 lakhs) only with the express approval from my brother. But my father has gone ahead and started with the construction of a first floor to the house without any intimation/approval from my brother, which is against the WILL and Codocil wrtten by by grandfather. My brother is now in touch with a lawyer who is working towards getting a stay order on the house construction. My questions are as below; 

1.) How much fees does it approximately cost to bring in the stay order to stop the construction work - towards the court (for the stay order) and towards the lawyer's fees?

2.) The original papers as per my grandfather's wish is in my custody. On what basis is my father contructing the first floor on the house? Can my father disregard his late father's registered WILL (in 1995)/Codocil and claim that he has inherited the house from his mother ? (As my grandfather after purchasing the house got it on his wife's name initially and then she transfered it back to my grandfather. However this old WILL is not registered). If my father does the same can his two sisters also claim for their share in the property (as they were born before 1960)?  

3.) If we bring the stay order, what possible counter actions can my father take? (My father has used some influence and has got the KATHA papers transfered to his name instead of tranferring to me, my brother and my step-sister as we are the absolute owners of the property. We have sent a notice to the BBMP on the same.

Please advice at the earliest. Thanks.