Very sorry to hear that. A couple of things that might help... First, in my opinion, the design of the fuel selection and gauging system on the PA-31 is very poor, and has potential to make life very awkward even for a competent pilot. While there's no way that NTSB or anyone else will recommend a re-design, they should be prepared to be critical of it, and of those who certified it. Second, it's part of the job of the investigator to help those affected by an accident to understand why it happened. Therefore, if you want to know more (and I would recommend that knowledge is a useful part of the route to 'closure'), then I would suggest that you get in touch with the NTSB and ask the investigator in charge to establish a dialogue with you. It may be that this is already in place with other members of your family, in which case, tap into that process. I hope this helps.