1. Since the property is in your mother-in-law's name, she alone can decide as to who should succeed to her property by executing a WILL to take effect after her death, to gift the same to any body(including her children) during her life time and can sell the property and enjoy the proceeds.
2. If your mother-in-law wants to execute a WILL in favour of her daughter, it can be done by her and she will be well within her rights. However her other non-beneficiary children can challenge the WILL in a court of law.
3. Since the property is in the name of your mother-in-law, it can not be termed as ancestral property.
4. In case she dies intestate(without executing a WILL), then all her children, i.e., your husband, his brother & sister will have equal share in the property - 1/3rd share.
5.To protect your husband's rights in this property, better to be in the good books of your mother-in-law.