Legal Question in Wills and Trusts in Illinois

The provisions of the Trust would not change merely due to your sister's residency in your parents' home. However, if your parents amended the Trust because of that fact, then the Amendment will likely stand.

Has your sister been taking care of your father while living with him for the past 2 years? If so, then she might be entitled to a "caregiver's claim" which could amount to a large portion of your father's assets which are OUTSIDE of the Trust. It's my understanding that a "caregiver's claim" cannot be applied to any asset that is owned by a Trust (including your parents' house), but I have not previously researched that issue thoroughly.

There is a method to "opt out" of your interest in your parents' Trust. To best protect your interests, it would be helpful to pursue this shortly after your father's death. However, I would caution you from giving up your share of the Trust like this. You may be able to work out a rental agreement with your sister or come to some other sort of agreement. Feel free to call me if you'd like to discuss this further. I won't charge for the phone call.

It sounds like you are not interested in the house. You just don't want the responsibility that comes with joint ownership of the asset. If this is the case, and you do inherit, then you can sign a quit claim deed conveying your interest to your sister.

If you are disinherited and you want your share of the house then it may become necessary to claim your share in court.