All US financial institutions, including credit unions, must comply with the reporting rules of the US Internal Revenue Service (IRS). To report the correct information, we need to know if a member and account holder pays taxes in the US. Form W-8BEN should be completed by members and account holders who are not US taxpayers. Form W-9 is for US taxpayers.
For Custodial accounts, the custodian needs to sign the applicable tax forms. For Youth accounts, either the minor or the adult joint account holder can sign.