You could file an quiet title action or a claim for adverse possession and see what happens. Normally the court will hold that you are all tenants in common and you cannot file for adverse possession except in unusual circumstances. You can file a lien against the property for the taxes you have paid and then file for a foreclosure or either file for a partition action. The problem is that then all of the property is sold at the courthouse door.
While it is difficult, if you are in the financial position to by out at least some of the others, that is your best route.
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