On the death cert it says she was 72, so that was wrong. But good spot re 76, I have looked at the record and although on the search result it states 72, it easily could be a 6 and not a 2.
Re Thomas, I noticed on some census records that some people were recorded if at sea, but it certainly may explain why they were in Ferry Port and then Charlotte and the kids returned to Montrose.
Thanks again