If you mean that you are a joint owner of the property, then you can demand reimbursement from the other owner for the reasonable value of the property, if he is allowing someone to live there without your consent. You could also evict the tenant, because as a joint owner, neither you nor the other owner can grant exclusive possession to a third party, without the other owner's consent. Therefore, the tenant is not lawfully in possession of the property.
Hope this helps.
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