Wis. Stats. 779.71 explains your rights and responsibilities. You have the right to dispose of the items after six months, but you must provide certain notices to the owners by registered mail. You must notify them at least 30 days in advance of the sale and afterwards, of any surplus funds. The owners of sold property have 12 months to claim the surplus.
The above paragraph is an overview. You must read the statute to determine what you need to do. If necessary, consult an attorney. If you do not know of an attorney, you can obtain referrals, including reduced fee referrals, from the Wisconsin Bar Association Lawyer Referral Information Service (LRIS)