How can I win a case claiming squatters rights?

There is no such thing as "squatter's rights"; what there is "adverse possession," which is the right to sometimes take over another's property if you are openly occupying it in a way hostile or "adverse" to the property owner's rights. However, you have to occupy it for at least 20 years (in your state) before the other side (the owner; in this case, your brother-in-law, since he is on the title) tries to remove you. In your state, you must occupy property in a manner hostile to the owner for 20 years before you can try to claim it. (This is because the point of adverse possession is to let some claim effectively abandoned property.) You write that you have been there for 19 years, BUT that your brother-in-law has only been trying to remove you for the last 4, since your husband's passing. That means that prior to that (for 15 of the 19 years) you were occupying the house with permission or consent--i.e. not in a way against or hostile or adverse to his interests. That means that at most, your occupantion has only been adverse for 4 yeears, which is nowhere near long enough in your state (it's 16 years too short) to claim by adverse possession. Plus your brother-in-law has evidently been trying to remove you for 4 years--thus, the property is not abandoned and he is actively trying to protect his rights. For both these reasons, you cannot assert adverse possession (or, as you put, "squatters rights"): you can't assert those right against someone who you have been trying to get the land from for only 4 years and who has been fighting you for that time, since the land had not been abandoned or neglected for 20 years.