Can I have a secret life insurance policy with the beneficiary as my brother so he can help my daughter just in case my husband won't be able to if I die?
Yes you can. A life insurance policy is a contract between you and the insurance company.
You can name whoever you want as your beneficiary/beneficiaries to your life insurance policy. I believe State law governing wills and estates does not apply to life insurance policies, so there's no rule that says you have to name your husband as the sole beneficiary of your life insurance policy, or even as a partial beneficiary to the policy.
You may be better off naming your child as the beneficiary to the life insurance so the money goes into a trust until she reaches a certain age.
Your will needs to state that your brother will be the administrator of the trust, if you want him to manage the money. That way, he is in charge of the money and can use some of it for your daughter, as needed, and the balance would be held in trust to be given to her when she reaches a certain age.
Here's an article that explains about the beneficiary of a life insurance policy.