Voluntary Manslaughter defined and explained with examples. Voluntary manslaughter is the intentional killing of another person with no prior intent to harm or kill.
legaldictionary.net
www.law.cornell.edu
Voluntary
manslaughter is a crime that occurs when someone kills another person with no prior intent to harm or kill, but under a sudden circumstance that made him mentally or emotionally distraught.
If, as you say in your post, they might have been murdered in bed asleep, that changes it to premeditated first degree murder.
So yes, where they were found murdered is an important question.
Was there a struggle when all 3 were awake and this was spur of the moment not planned? Or did the son plan ahead - planning under the cover of darkness - to sneak in and stab them while they slept in bed?
2 Cents