Names and numbers not showing up in SMS history
When I look at his sms history, I see MMS, what is that? Also when he sends a message sometimes it shows as "insert-address-token". Also many messages the just say "null". What is that?
MMS is Multimedia messaging service. https://en.wikipedia.org/wiki/Multimedia_Messaging_Service
You can have pictures, videos etc. in a text message.
Not sure about other things you mentioned. I have not seen them myself.