I would explain to them if they wanted equivalent Disney accommodations, it would have cost $3,000-$4,000 more. I am not sure what size room you got, but the lowest category equivalent to it at Disney is a 1BR DVC room. I simply picked my dates. A 1BR at SSR is $3,913. My 1BR at WBC is $560 ($3,353 price difference). Both have kids activities throughout the days, ping pong, billiards, pools, and pool slides. WBC has 2 lazy rivers, mini golf. SSR has onsite buses, movies, FP 60 days out, and EMH.
For $3,353 savings just for the room, I can do a whole lot at WDW. Yes, can you cut that savings down a bit going through a DVC owner? Yes, but it will still be $1,500 -$2,000 more. I would just sell it to them on the amount being saved. If they don't enjoy it, you can always go back to previous plans the next time.