My exhusband and siblings created an LLC for property inherited last year. Does he have to report the income to child support?

Your ex spouse's inheritance is ordinarily not considered income for purposes of paying child support or maintenance under Wisconsin law; similarly to going through a divorce, a gift or inheritance received from a third party, is exempt from property division; however, once he receives his share from the estate and invests it, the dividend and interest income received from the principal can be used for child support purposes. Also, in the event that he is not working or has considerable child support arrears, in that event you could petition the court to request that some or all of his share of the inheritance be set aside in a trust for you to draw the money out for payment of either back support owed or for current monthly support; that motion should be filed promptly, before he gets his hands on the money, to avoid it being dissipated by him, which would defeat the purpose of going after it in the first place.