OK; if steps are working then the chassis latching relay is operated and is supplying 12vdc to the chassis battery load bus in the BCC schematic. Note that the schematic is dated so there may be loads assigned on the schematic that may have changed assignments by 2014. You will likely need to very carefully check fuses in the BCC to see if they are 12vdc powered and/or blown. A digital voltmeter is a great tool to have for this situation (and a 25 year old spine to contort into position for access into the BCC). No rings; no watches if you check fuses live.
Regarding not charging the coach batteries when driving (via alternator) and not charging chassis battery from converter (when on shore or gen), it is “likely” that the interconnect relay, or its contacts have failed to close properly......thereby not connecting coach and chassis battery strings to each other as required. (You mentioned that the converter does charge the coach batteries OK, so the 50 amp mini breaker shown on the left side of the BCC schematic (House Panel connection) and coach latching relay are likely OK.
If you go onto the RV Custom Products web page they provide the schematic and very good operation/testing documentation for this BCC.
https://rvcustomproducts.com/fw-2050
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