If you can display them in a form, then you can add them up.
Try using the Data Viewer and experiment.
Wouldn't adding the fields directly work for you?
TOTAL_BUSINESS + TOTAL_OWED + .... + TOTAL_NET_WORTH = a number?
Sum ( Bank_accounts::accts_total;
Assuming each of the fields in this list is a number field, not a summary, just replace all the semi-colons ( ; ) with a plus ( + ) and delete the final semi-colon.