When I put more than one person as the recipient to my message my Samsung Galaxy S3 vibrates and says it's converting to MMS. When I send my message I know at least one person is not getting the message. However that person can send me a group message and I can see it is as a SMS instead of MMS.
I can't find any options to prevent it from becoming a MMS. I set the delivery report checkbox and sent another one out. I know one person got it and that person did it. I get no report on who got it. I'm using Android 4.3.