Validity of registered WILL in the court

Housing board Haryana allotted house to Mr A Mr A applied to transfer house in the name of Mr B , official ask A to come in person with his sign attested by a magistrate (objection being signature) Now Mr A appear in front of the concerned authority give his affidavit.Mr B is in blood relation of Mr A.Housing board Haryana approved the application and issue a letter in this matter. For some reasons final letter is not issued and house remain in the name of Mr A .As Mr B and his family has been supporting Mr A in the past keeping the relation Mr A got Registered WILL and also registered GPA in the name of Mr B. Mr B live abroad and Mr A died. After the death of Mr A one of his son give copy of the death certificate to the father of Mr B for the purpose of property transfer. After few years Mr B apply to Housing board to transfer the house on the bases of this registered WILL.Housing board published in the two local papers no objection surfaced with in the time but the housing board issue letter to Mr B to get letter of probat from court so that further action can be taken. Mr B filed writ petition in high court, now Mr D son of Mr A file case challenging the WILL and also got a GPA in his favour from his brother Mr K who live abroad as owner of the house. Mr B and his family was living in the house and Mr D took the advantage and trespassed the house and rented it out. In the court documents they never said when they entered the house,but have stated Mr B is A stranger to the house,Mr B was a short time licensee, Mr B never lived in the said house Housing board also given some false statements. What is process in the court to follow to prove the validity of the Registered WILL. Please email me your advice