I can offer Facebook two choices to verify death if a third party alleges it. Either provide the death certificate or the name of the funeral home.

If Facebook was smart they'd make it super simple for the funeral directors to provide this information directly to them. I lost my dad late last year and had to answer a number of questions for the funeral director.

All the funeral director would have to do is ask if the deceased had any social media accounts and do you want me to contact them on your behalf?