Greetings GroupingText,
Being able to manage the contacts you're sending messages to is important. To confirm, did you create these groups via iCloud as outlined in the following article? If so, you can learn more about adding and removing people from groups via that article.
Create and manage groups of contacts on iCloud.com
If you're looking to add or remove people from a group message that already exists, you can do so via the steps listed below. You can also find these steps outlined in the following article.
How to remove someone from a group text message
- "Tap the group message that has the contact you want to remove.
- Tap the group icons at the top of the thread.
- Tap the gray arrow icon to the right of the contacts, then swipe left over the name of the person you want to remove.
- Tap Remove, then tap Done."
Add and remove people in group text messages on your iPhone or iPad
Have a wonderful day!