Dividing Share Certificate between two Brothers

My parents had purchased a flat of a co-operative housing society and both of them are the members of that society (Share Certificate having both of their names). Now last year both of my parents had passed away. Please note that my parents didn't register anyone as nominee. I have a brother and we both want the equal portion of share to be transferred against our name. But as per the co-operative lawyer, as per the rule, the share certificate can not be transferred and divide between two brothers. As per him it can be only divided between mother-son, father-son, husband-wife. Although he said that we both will be owner of the property. He also informed that the person for whom share certificate will be transferred will be also registered in the Mutation. So my questions are as follows: 1. Is it possible to divide the share equally between two brothers? 2. How the other person, who don't have his name neither on share certificate nor on Mutation can be joint owner of the property? Please let me know your advice.