Sale without cosharer

File suit against them not to alienate and take injunction in civil court immediately.

Even if you agree to such a sale unless you contribute with your signature with the eligible share the sale may not be valid.  You can get a lumpsum amount and may invest in the post office and you can certainly get a better return on such sale proceeds of your share when compared with the rent you have been receiving..  The details are not adequate as to how, and why you are receiving rent on your husband's paternal property, who is having such legally valid title deed of that property, and your right to claim rent on such property.  Contact a local advocate and discuss with him.

It appears the property belongs to the parents of your late Husband and your Mother in law is not in good health and may not be of sound mind. From the fact that you are able to collect the rents and the family is not objecting to it or trying to disrupt the arrangement which was followed prior to the death of your Husband, the relations with the family are presumed to be good and amicable.  Therefore, you may have a family meeting in the presence of Elders and get the matter amicably settled ensuring that you get your share of the sale proceeds if the sale of the property is indeed being attempted. If that is not possible or not happening, you may approach a capable and reliable local Lawyer with full details and get a notice issued to the family members not to proceed with the sale without your consent as Minor's interest (your Daughter) also is involved. If need be an Injunction need to be brought through the Court preventing the sale.

Under the circumstances, if the sale happens without your getting the share, the transaction is open for litigation and the buyer is at risk of getting the sale being questioned in court by you along with other claimants if any.

Your name is, admittedly, Dubyendu Das and a male person. Why you are seeking remedy pretending to be a different person, that too a lady?