Who is the interest being paid to? If it is being paid to a beneficiary named on the policy, then that beneficiary had to have taken some action after his death, and would have elected at the time to keep taking the interest payments and not cash in the death benefit. And that beneficiary would have every right to know what that death benefit (the amount of the policy) is.
However, if the company was never notified of the death and is making those interest payments to your father, then whoever is/was responsible for his estate is signing those checks as executor, or someone is committing the crime of forging your father's name. The executor also has the right to know the amount of the death benefit. Met Life would not refuse to give this information to the beneficiary that filed the claim or to the executor.
So, something about your story doesn't quite add up. There's this, too. If the interest is paid weekly, then why will another check not be coming for another 15-30 days?