Guardianship to grandparent upon death, instead of spouse

My husband and I separated recently and are in the process of negotiating a separation agreement, where I will get physical custody and he will have visitation. We have 2 young daughters. My husband has a bad temper and my daughters do no enjoy spending more than a day or two with him. I am going to rewrite my will and want my mother to have guardianship of my children if I were to pass away. Can I do this? Will the court automatically grant full time custody to my husband if I were to die? My girls have consistently said if I were out of town for a week or a few days they would rather stay with my mother rather than their Dad. Is there any way to ensure my mother could get custody at my death?

Changing your will doesn’t prevent the children’s father from becoming the custodial parent in the event of your death. Even if he wasn’t the primary caregiver or custodial parent, there is a legal presumption that that surviving parent is now the caregiver and that he has complete parental authority.