In general, families are allowed access to evidence to the extent that it is helpful to the investigation. For example, if LE had a voice recording and could not determine if it was a victim, the victim's family may be asked to identify their daughter's voice. LE can often do this themselves by comparing to a sample. Once a suspect is in custody, the victim's family may be given more information. But they don't have a strict "right" to information either.
In my experience, LE always gives the victim's family a heads up before anything is released to the public. A good and community-minded LE would personally go over what is going to be released with the family first. No one wants to shock or upset an already grieving family. You hear stories about families being blindsided by a release but IMO that's often a leak through a journalist, or an LEO not following best practices.