Massallah pertaining to who to choose as ones childrens guardians

I have a r year old son of and a 1 year old daughter. I would like to know who we should name as their guardians if my husband and I were both to pass away. My mother and father are both alive but divorced and I have 3 older sisters, all of whom are married. My husband’s mother is still alive and he has 4 brothers who are all married. My husband and I cannot agree on a guardian. Please include a reference to what Islamic Law we should look at as a basis for our decision. Shukran.