Guardianship of Nephew in California?

My daughter is 22 years old and I would trust her with my 9 year old any day over my 40 year old sister. It all depends on how mature the 21 year old is. They are perfectly capable and since they lost both their mom and dad, maybe they feel they are all they have now, each other. I would let him try and take care of his brother. Offer baby sitting, cooking, any way you can help. Stay in his good graces, if then you find that he is in over his head, offer for the boy to come live with you. I think it's pretty admirable for a boy 21 to want to take on his little brother. He loves him a lot I'm sure. Let them try and be a family, they've had a lot of loss in their young lives.