Without knowing the context of the situation - namely the circumstances of the event, what lead up to it, what kind of relationships the girls had (were they happy and supportive or were they living in abuse or neglect?) - it is impossible to really to make conclusions.

I do however agree with the comment that their mental illnesses must be considered to be unmanageable in order for what appears to be the maximum penalty.

Sociopathy and psychopathy come to mind. Can one really recover from these things; especially when such an extreme act has occurred? In my own opinion these things cannot be fixed and I am not so sure I want someone who has acted accordingly responsible for their own lives such as the taking of one's medications (you can't force that on someone here). The recidivism of such extreme examples on release is high.

Thus, on the surface of this situation, I am inclined to agree with such a sentence.

I am still inclined to believe one does the punishment that befits the crime.