Is Donepezile, Memantine (Namenda) and Divalproex a good combination of medicines?

A good person to ask would be your pharmacist. If the pharmacist has concerns then discuss it with your husband's doctor. Even if there are concerns, the doctor may have concluded that the risk of drug interaction is small compared to the risk of aggressive behavior. But at least then the doctor could explain it to you. Sometime doctors are wrong, but sometimes they have good reasons for what appears wrong. It is good to check this out with each new drug.