Getting Cr. & Dt. Trans Statements Of Expired Father SB A/c Pass Books

Our father was a SBI employee. He opened & operated more than one a/cs. in SBI. He was the Primary Account Holder of these a/cs. We (1 eldest male, 1 younger female and 1 youngest female) are legal heirs, educated and married. I think, he nominated our youngest sister as Nominee in all these a/cs. She is also a JOINT A/c holder in one of these a/cs. Now he is no more. The youngest sister captured all the A/c Pass Books and ATM Cards. She refused to give them to us for our understanding. I have her JOINT A/c No. only. Hence I met Personal Mgr. of the branch to get the Cr. & Dt. trans statements of Pass Books but he asked me to come with other two sisters to get it. Later I sent a RTI letter with legal heir certificate & my Voter ID card xerox to the bank reg. this through Reg. Post. But no response from the bank except Ackg. Card. Sir, How to get the statements from the bank with(out) court intervention. Thanks,