How can I get the monies from my grandmother''s estate when my uncle, the executor, is not being honest about the estate & has put off doing anything?

My grandmother passed away April 2010. My mom died in May 2009. I am the executor of my mom''s estate. My sister and I are the beneficiaries 50/50 for my mom''s estate. Before my mom died, she made it know that her mom had a nice retirement and other funds. My grandmother''s will states that my mom and my uncle each should split estate 50/50. My uncle, my sister, and myself are all owners of my grandmother''s home (50%/25%/25% respectively). Home in PA. My uncle has only told us about one small life insurance policy of my grandmother''s but has refused us knowledge of any other monies of her estate. He moved into my grandmother''s house about 3 months after her death, just informing us he was doing so. He tells us he cannot pay us our 50% interest in the house because he can''t get a loan. He tells us there is no other monies because Medicaid is trying to collect money. We feel he is lying and has been hiding money and information on the estate. What are my rights and what should I do?