A mortgage protection insurance policy provides you with life insurance and disability insurance to pay for the mortgage in case you become disabled o die.
The insurance proceeds go to the mortgage loan company, not your family.
Mortgage protection insurance does decline over the life of the policy, in-line with your decreasing mortgage loan.
Another option is decreasing term life insurance that pays out a death benefit to your family, and the life insurance amount declines over time with your mortgage loan, but the premiums stay the same each year.
Still another option is level term life insurance which provides a death benefit to your family if you die. The amount of life insurance and the premiums stay the same each year through the duration of your term life insurance plan. Your family can use the death benefit any way they choose, including to pay off the mortgage, pay for living expenses, replace your income, etc.
Here's how you can learn more about mortgage life insurance.