do you have a favourite musical genre/movie type/author? That can work well - get everyone to dress up, play appropriate music, serve appropriate food etc.
Why do you want games? To entertain the LOs? If it's your 21st I'd keep the focus on you and let any DCs who are present almost have a seperate party - you could hire a clown or musician or jumping castle or just stock up on age appropriate games and activities for them elsewhere?
Adult bouncy castle would be awesome but have no space in garden! There will be quite a few of us I think, isn't murder mystery an 8 person limit??? Or do you know of any that have more people to play?