3 siblings own a home, one lives in it pays the bills and has made improvements but refuses to buy out the other 2 siblings.

The other siblings can file a partition proceeding. The Clerk of Court will appoint a commissioner to partition the property (or in the case of property that cannot be equally divided, sell the property) and divide the proceeds among the owners. Be advised, that often properties that are sold pursuant to partition proceeding sell for less (sometimes far less) than market value, so all siblings would likely be better off if the sibling that is living there refinances and buys the other two out.

I agree with Mr. Faucher...force his hand by threatening to file the action and make him refinance. Or....as a part owner you have the right to equal access to the home. "Move in" whenever you like and be an annoyance to him...nothing illegal though.