Since my dad passed away in 2009 my sister has been living on the property. There is no mortgage and all she needs to pay are the taxes. Back in 2014 my cousin pay $2500 for back property taxes. My other sister and I have tried to get my her to sell the property but she won't . Now she owes $9400 in taxes. What can I do legally to get her to sell the property?
What can I do legally to get her to sell the property?
There's not a way in any jurisdiction that I know of to force her to sell. One option would be to wait for the natural consequence, which is the county (or applicable jurisdiction) foreclosing on the property for payment of back taxes.
If she's content with that outcome then I don't know that there's much else you can do. At that point, you could try again to convince her to sell the property to a family member at least, or risk letting it go at auction. I definitely would not pay any more of the taxes for her as it's just postponing the inevitable.
If she doesn't pay taxes then eventually the house will go to auction.
Let's say the house is worth $200,000. So the highest bid should be $200,000 but would probably be less. Then the tax would be paid out of this, and everyone gets one third of what is left.
If you want to then you and your cousin together could bid say $210,000 for the house. Then the tax would be paid out of this, and you and your cousin get one third each, that is $140,000 minus two thirds of the unpaid taxes. Now the house is yours for around $70,000.
A nasty method would be for you and your cousin to move in. You can't throw out your sister, because it's one third her house. But neither can she keep you out. Your family relationship will suffer, but I assume it's bad anyway.