Danielle Gibbons notes that her family has a single Apple ID/iCloud account, “and we keep getting each other’s text messages. How do we stop that from happening?”
Unfortunately, an Apple ID and the associated iCloud account are a single entity—there’s no way to split out multiple, different text messaging or iMessage delivery addresses.
However, it is possible to use third-party messaging apps, like WhatsApp (free, iTunes Store link), and third-party apps that handle sending and receiving text messages, like Text Free, because you can set up a unique account with those services.
Read more here:: When sharing an Apple ID creates iMessage and text message confusion