It would help if you can draw and post a sketch so were all working from the same picture.
Also post the signal level report and event log report pages from both of the modems. We can tell you how to collect those.
First Question: Why TWO data modems?
TWC onlyallows one modem and one public IP address per residential service cable connection.
Second Question: Did TWC say that you needed an amplifier? Did they install (and therefore now maintain) it for you?
Third Question: Where and why do you think MOCA fits into this?