Can i (and how) deduct a defaulted personal demand loan to a family member? It is documented and I have charged interest which has accrued to this point.

You might be able to claim a capital loss as a result of this loan. You should consult with the CRA to see if you can do that. If you are in Canada or the United States, you can call the CRA at 1-800-959-8281. Here are more ways to contact the CRA: https://www.canada.ca/en/revenue-agency/corporate/contact-information/telephone-numbers.html