Right now, your Mom has a regular income from this property she owns. If she quit claims, she has no income from nor investment in the property. You get a serious bonus (a free house) without waiting to see if you will inherit it.
My first question is this: is the rent you pay the going rate for a property like this?
The rest of my questions can be answered by your Mom and a tax consultant/CPA. What does she, the owner, want to do besides having you as a tenant? What are the tax implications for her of any transfer of title? What is in her best interests? What is the fair market value of the house?
Why do you mention repairs? As the landlady, ask her to make them.
Talk to your Mom first.
I would normally not answer such a specific question about a locale I am unfamiliar with--I just wanted you to know that we don't have a lot of real estate pros regularly participating on "Trulia Voices" from WI right now ("Voices" is really new--help us spread the word!). If the market prices are stable where you are, I venture to say it is probably better to buy than to rent. How you transfer the title from your mom to you and your sister can have major tax implications--even a local REALTOR may not be able to provide you with the best advice--you should consult a CPA. The bigger problem with your question is how to hold the newly transferred title with your sister? What if one of you needs to move, gets married, passes away (god forbid), etc? They legal ramifications of sharing title with a person other than a legal spouse are absolutely daunting! I would recommend that only one of you purchase the home; and then reach an amicable financial arrangement for the "tenant." I hope that helps! Best wishes!