Welcome to the community! I was able to test the People option on the phone. As you access your groups you would then press menu and there will be an option to "delete group member." Simply check off the contact to remove from group and click delete. Unfortunately, you are not able to add more than 10 people to a groups through the native contacts app. Please let me know if this resolved your concerns.
Do you have your contacts in your G-mail account? If so, just go to your Google account and make a new group with as many people as you would like. Then, when you click on the People icon, this group will show up, and you can message everyone in that group at one time.