If your father has not passed and the house is in his name, regardless of what the will states nothing can be done unless you are your father's agent under a POA and even then you need to have an attorney review it as to options. When your father does pass, if he is still the owner, and the will leaves the house to each of you, and she was living there when he died by his invitation, she cannot be evicted. You would, if you are the executor, have an attorney file a petition to eject her and legally so long as she cooperates with showing to prospective purchasers it she does not have move, pay any utilities etc....As to unpaid bills while living there when her name is not on the deed, you dad would have to file to eject her. Of course, if she can be convinced to sign a lease and then she breaches you could proceed in landlord/tenant court instead which is a lot cheaper. If your names are already on the deed, you may be able to file to Partition the property and force the sale. Once the house is sold, if done when your dad passes, the net proceeds would pass via the will. So you need to have an attorney review all documents to discuss what should happen and what steps to take now and in the future.
Once the house is in the name of you and your sister after your father passes away, you can petition the court to partition the property. Since the court can't divide the house in two, it will need to be sold and the cash will be divided.
I agree with my colleagues that this is going to be a messy situation. If your father is still living, there may be other options that would make better sense. You should visit with a lawyer to see what the best option would be for dealing with this.
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