Yeah, I considered making a game about killing zombies instead or your family members. That may have been better perceived. However, I dismissed this for two reasons: The first one is that it would diminish the impact: Each family member has a different background and really wanted to highlight their personality. Zombies are... zombies.
The second one is that the description says that both the theme and restriction are open to interpretation. I'm the kind of person that likes giving things a twist, so instead of going the normal path, I thought it would be cool that the restriction references the winning condition: After you kill your family, there are no living things left (remember you're on your deathbed, so you're as good as dead).
Thanks for playing though! :-) Hope you liked it!