Legal Heirship Certificate

My husband died four months back due to Cancer. After marriage myself and my husband separated from his family. I am not having father-in-law only mother-in-law and 2 brother-in-laws. After marriage my mother-in-law sent us out. but still she and her other two sons are staying in my husband's residence only. I have spent huge amount for his treatment for the past 1 year. I kept all the medical bills my husband's phone and laptop at hospital. His brother's stolen the laptop bag along with his mobile and medical bills. After his death i cannot able to claim the medical bills. two months' later i got a call from my husband's number and my brother-in-laws talking unwanted talks and torchering me over phone. i have recorded all their talks. I have given police complaint and got CSR number also. Police taken action after heard the record and they collected the mobile from them and given to me. They given the statement to police that the Medical bills and laptop they lost somewhere. now i went my husband office for claiming his PF & Gratuity, but at the same time my mother-in-law also coming for the same. In his office advocate sent legal notice stating that whoever is coming first along with legal heirship certificate they only get all the benefits. Is it possible to get Legal Heirship Certificate without my mother-in-law name? she already having two sons apart from my husband. but i am not having children also. Now i am alone. Still she is staying in my husband's residence only. kindly suggest me if she can get legal heirship certificate without my name, how can i challenge the same? if i get legal heirship certificate, it is worthy / valid or invalid. Office is ready to give claim, who is coming with legal heirship certificate. If i got legal heirship certificate she will be challenging my certificate? please advise. I am not working anywhere i dont have an income. I am staying rental house only. my father and mother aged and no income for them also. My mother-in-law having properties at Chennai. My father-in-law's property but she is not ready to give that property to me or my husband. He requested to give the share of the property earlier before he dies for his treatment, but she refused to give. Kindly suggest me what to do in this case?