Bar
big stack of plates (get 3x the small plates you think you want and half the wheels)
Rack / cage
Adjustable bench
Everything else is a waste of space. Mountain bike > assault bike. Sidewalks > treadmill...
Discussion
This is kind of where I am now. Minimalist gym but thinking of things for kids and wife too
Preteens don't need "equipment". Put them on a bike, and convince them climbing trees is fun. Real life should supply most or all of their exercise needs.
Our weekly family ride is the highlight of all of weeks. Quality,screen free time, fresh air, sunshine. There is absolutely nothing negative about it.
We do those things now, thinking I'll add a climbing wall in here and they do pull ups now