IMHO, asking for a firewall for a non-tech savvy family is like asking if there is a safe power tool for children.
Am gonna be brief. These says, bad guys don't need to attack you front-door (what a FW guards), they do much easier things like Phisting. Entice your non-savvy family family to click a bogus site and BAM! they are in, and no FW will save you from that.
If you are helping these folks, force them to maintain backups, and if I was going to do this, OS Image Backup of each machine in the house. No complaining they have to buy a backup NAS, otherwise am out.