Control iMac using Macbook Air keyboard and mouse?
If you are fine with using your iMac as a display with your MBP doing all the work, enable Target Display Mode.


  
  Make sure that your iMac is turned on, and the other Mac is logged in to a macOS user account.
  Connect the Mini DisplayPort or Thunderbolt cable between the two computers.
  Press Command-F2 on the keyboard of the iMac that you want to use as a display.
  


If you want to your iMac to do all the work, you could use thunderbolt networking and then use some of those apps that you tried earlier with wifi. To set up thunderbolt networking, just follow the directions here.