LEGAL HEIR CERTIFICATE IN CASE OF DISPUTES

SCENARIO- Due to  the death of father, legal heir needs to file income tax return of the deceased. For this, one needs to apply for legal heir certificate but due to disputes other siblings have refused to sign or give any details needed to apply for respective certificate. There is no will left behind. 

How can one apply for legal heir certificate or is there any other way to proceed with so that the deceased income tax return can be filed.