You should consult a lawyer on your daughter's behalf to see if there is anything that can be done while she is in the hospital.
Since your daughter is still married, she and her husband have the same rights to the children. Also, since she is in the hospital and unable to care for them, he has legal responsibility for them. Unfortunately, I don't think there is any way to change that or force visitation without a court order. So, consult a lawyer.