The Smith Estate is represented by JABberwocky Literary Agency: [
awfulagent.com]. All inquiries regarding game licensing should be directed to them. I would also suggest that you research the copyrights of the original appearances before contacting them. Be warned that they also represent Arkham House. Arkham House had some very negative experiences with gamers a while back, and that has not left them with any warm, tingly feelings toward new proposals. I would suggest that you make any proposal as specific as possible without waxing prolix.
Good luck.
Scott