1. Have you obtained grant of probate from the Court for claiming the title of the house bequeathed by your mother in law to your husband?
2. Without the grant of probate, th will has no value more than a scrap paper.
3. After obtaining the grant of probate, your husband can lodge a police complaint against your sister in law accusing her for physically assaulting him and then obtain a Court order restraining her in entering in to the house standing in the name of your husband.
4. If there is no probate of the said will obtained from the Court, she can claim her share on the said house being the legal heir of your mother in law.