There is nothing illegal about it, it is just in bad taste. Since she is your sister, why not have a private conversation with her and say in a non-confrontational manner "Sis, it makes me and Charlie uncomfortable when you discuss his finances with others, even though they are family members. Would you mind keeping it private?" This is one of the hazards of doing business with family.
Answered on Feb 25th, 2014 at 4:54 PM