Is a "Takaful" document, which involves paying a monthly sum for 15 years, with a variable interest rate ranging from 7% to 12% calculated upon receipt of the amount after the term ends, and the deceased's family receiving a sum of money in the event of death before the term ends, permissible or forbidden?

The transaction mentioned is a forbidden usurious loan, because the bank is obligated to return the amount with interest. Additionally, it contains commercial insurance based on gharar (excessive uncertainty/risk). The legitimate formula for investment is for both the capital owner and the bank to have a common and specified share of the profit, without the bank guaranteeing the principal capital, because the losses are borne by the capital owners according to their shares.