Good evening. I can understand your frustration over this situation. But, you are not without options.
First of all, if you both own the house, then if your sister (or her designees) are living in the house, then you are entitled to 1/2 of the fair market rental value of the house in excess of 1/2 of the costs of the house. If you are both already splitting the costs of the house....such as insurance, taxes and maintenance...then you would be entitled to the 1/2 of the rental value without deduction. You could demand this be paid, and if it was not paid, bring a claim for this.
Second, what happens to her 1/2 of the house upon her death depends on how the title to the house is held by the two of you now. If the title provides that you own this property as joint tenants with right of survivorship (or similar language that references that it is transferred upon the death of one of you), then when your sister dies, title automatically vests in you. If the title does not contain any "right of survivorship" language, then the two of you basically own undivided 1/2 interests in the house as tenants in common. In that case, your sister's 1/2 interest goes to your sister's heirs.
Third, if your sister's 1/2 goes to her heirs, you are not forced to forever own this house with them. If they will not agree to either sell it, buy your interest or sell their interest, you can bring a partition suit in which the court will order the house sold and the proceeds divided.
Fourth, if you can prove that your brother in law simply took things in the house that at least belonged one-half to you, you can file a lawsuit against him for 1/2 of the value of these items.
I hope this has given you the guidance you were seeking. I wish you the best of luck!
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The information given here is not legal advice. As all states have different intricacies in their laws, the information given is general only. This communication does not establish an attorney-client relationship with you. I hope this answer has been helpful to you.