What happens when someone passes and leaves you a house?

Ok so my great uncle has a house legally in his name and I and my sister live there. Legally I am not sure if I'm in his will but he has said verbally he is leaving me the house (the last person on paper for the house to be left to was my mother-- that was on my great grandmas will, but it was left to her son). I however am in a sense concerned because my sister does live here, neither of us pay rent, and anyways he's leaving it to me, not trying to sound in anyway messed up but he's got at least another 10 years, but retiring in a few years and he has enough in the bank and I'm slowly building my account up. The mortgage he says should be paid off soon, it's only $600 a month, and of course the regular bills and whatnot. But I'm just wondering, my sister is just a very one way stuck up person and we have our differences but if he leaves the house to me, and my sister is still living there, how would I go about escorting her out? Again no one knows the circumstances here so don't assume anything but I just want the house to myself and want to live by my own rules and eventually have a family in that house. My sister basically lives with her boyfriend now and only stops here sometimes as she's in college and works. Also from what I've been told, she doesn't want to live here as she gets older, she doesn't like the house anyway. So I live in Massachusetts, are there any types of laws governing this? Thanks.

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