It may very well have been family members. I'm just saying that, where I live anyway, it would not simply be a matter of innocently checking a box and returning the ballot on behalf of dead grandpa. It would require either deliberately requesting an absentee ballot, providing all the requisite information, or appearing at a polling place with i.d. to cast a fraudulent vote. That isn't something innocent or excusable -- it is deliberate voter fraud, a third-degree felony in our state, punishable with a fine of up to $5,000 or five years in prison.
I can't imagine doing that, no matter how much I love my parents or my spouse, no matter how strongly they or I feel about an election. Can you?