How do I send the same message to multiple people

You would have to send the message in a Group Text.

Send a group text message

1. Open Messages and tap the Compose button .
2. Enter the names or tap the Add button  to add people from your contacts.
3. Type your message, then tap the Send button .

Axel F.

That would be a group text message, which this link explains how to so --> Send a group text message on your iPhone or iPad - Apple Support