How strong are credit unions in providing international banking services compared to large banks?

Credit Unions are domesticated banks. They work best within the US, and don't have much dealings and/or business internationally. They rely on partner banks and correspondent banks to provide international banking services and facilities. If you will regularly be sending money back home, your best options are to turn towards remittance companies like Times of Money, Remitly, TransferWise, Xoom, etc.