How can we transfer property without legal heirship certificate?

Both of my parents have passed away. My brother and I are their only children (we have documents such as ration cards and birth certificates to prove this). My mother was the sole owner of a property (a flat in a registered co-operative housing society) located in Maharashtra. She nominated both of us as beneficiaries, with each entitled to a 50% share in the property. The society’s legal advisor has asked us to produce a legal heirship certificate in order to transfer ownership of the flat in our names. However, obtaining this certificate is quite expensive. We are therefore seeking a less costly alternative. Kindly guide us on the alternative legal options available to transfer ownership of the property in the absence of a legal heirship certificate in cases like ours, and please mention the relevant legal provisions that support such alternatives.