Mutation/ relinquishment

My father's first wife died after say 1 year soon after giving birth to a male child My father was in railways and often touring grand mother was not interested in looking after such a small kid so father has decided to marry again and he got married second wife took care of that child with best care later on family grew bigger with 4 more kids time passed everyone is settled in his life and doing well i am one of those 4 kids our father was given a small 2 room house by my grand father which he sold and spent the money to marry all children.time flew father bought a society flat from his savings and PF money and started living with his wife happily all children left them and started living separately, i have purchased a flat nearby so i kept visiting them and they also, then i have shifted to Jaipur and my parents kept vising me they normally spent their all winter sessions in Jaipur with us. Father had an accident and broke his hip bone after which his health deteriorated slowly that time i was in Kota, Rajasthan. my mother's health was also not good she was suffering from arthritis in knees then a took them to Kota with me and took care of them even a lost my job but they were stayed with me happily. My eldest brother SB( name changed, kid from first wife of my father) was least bothered about them never cared about them, never visited them,never asked them for any thing financially they were not dependent on us or anybody else. In 2015 my father died because of many medical conditions and in his last days i somehow managed to get a WILL prepared (in the favor of my mother), signed by him and by two witnesses, but it is not registered. Now i m taking care of my mother, my real brothers n sister keep visiting her at my place now the scene is that SB is not signing for Mutation in the favour of my mother. In society records my mother is the nominee and they have Xferred the share in her name now my Q is, is there any way to mutate the prop in my mother's name and secondly can he (SB) challenge the WILL on medical grounds thirdly can he get a share (keeping in mind his negligence towards his parents) and can we go for probate on will thru court and lastly is there any way sell off the prop with his disagreement