It may be tough for the family, but the decision on the DNR form is made between the patient and their physician. Relatives disagreeing on what’s the best course of action is not a reason not to get a DNR form. Only the patient has the right to make decisions about their health care.
The only way a DNR form can be refused to a patient in need is if they show signs of depression or cannot fully comprehend the treatment options if they're not of sound mind.