2 copies of the texts : this is not an issue.
If you send message between tmo to tmo which supports chat and read receipts, there is no issue. Ony tmo to other carrier, it looks like 2 text momentarily but 1 only. Its because of RCS feature that tmo supports.
Try turning off group conversations (sends every message as group conversation by default)
Messages app> three dots> more settings> multimedia messages> group conversation
Well what does it mean when you send a message.. A in notification pops up in a box saying a report will be sent. And this only happens to certain people that you sending messages to?