You can deduct the unpaid principal if you can show that the debt is fully worthless. The fact that the borrower filed for bankruptcy does not automatically establish worthlessness. However, even if you can establish worthlessness, you can only deduct the unpaid principal. As a cash basis taxpayer, the interest you were to receive was never reported as income so no bad debt deduction is allowed for this amount.
A joint tenancy in real property in the name of both husband and wife. On the death of one tenant, the survivor receives entire interest.