Mortgage protection insurance is designed to pay off your mortgage if you die, not to provide a cash sum to your dependants. So, you’ll usually need separate life insurance to provide a cash lump sum if you have a dependent family.
You can, if you want, use an existing life policy for mortgage protection by assigning it to your mortgage provider, so long as the amount you’re insured for is at least equal to the value of your mortgage and it runs for the same term. Should you die before the life insurance policy ends, the mortgage will be cleared and the balance paid to your dependants.