Can the 4th party claim to have title in the property ?

i am the title owner of a property with 50pc share. 2 other people have 25pc with someone and 25pc with someone. i have the possession of the property since 12 years and others have it since 50 years. now few people come and park there bike and go. i have told them not to park. they start fighting. the house is on rent the, the tenants have no problems but its someone else who is claiming to have the rights in the property. i have called the police and towing van as well. but it is repeated again and again. in this case what can be done?