How do I send money to family?

See the information in Send and receive money with Apple Cash - Apple Support

but note the following requirements from that support document:

You and the person that you're sending money to or receiving the money from must:2

• Have a compatible device with the latest iOS or watchOS.
• Use two-factor authentication with your Apple ID and sign in to iCloud and iMessage with the same Apple ID on any device that you want to use to send or receive money.
• If you're sending money to someone, make sure there's enough money on your Apple Cash card or an eligible debit card in Wallet.