Can a co-owner force someone off a shared deed?

In some states, a co-owner often can force the sale of a shared property by filing a so-called partition action. In such a situation, if the severance is granted, the property would be sold and the owners would split the proceeds proportionate to their interest in the property.
You should check your title for any references to such a severance action. You may need to consult a real estate attorney.