Would a rule such as having flown with the other family plan members on the same PNR within the last 12 months work to deter things? You'd need two brokers to go with each other to make that work.
ie if I haven't flown with my wife or other members in the last 12 months on AC on the same PNR we cannot book an individual or group reward ticket.
I feel like if people have large family sharing legitimately they will have all flown within the last 12 months in some form of combinations together.
Just spitting thoughts as I'm annoyed about this.