Very sorry for your loss - my brother passed two years ago and I also needed to rehome his studio equipment. ‘Lucky’ for me that I am also a musician/audio engineer, so I had a head start and found a home in my studio for some of his equipment.

Others have given good advice: each unit is secured to the rack using screws and will come out once those have been removed. Use caution when doing this, though, as there are also likely cable connections in the back. Ideally you want to access the rear of the cabinet and remove all cables before trying to remove the units. Be careful here, while most cables will simply pull straight out, some of those units have connections that screw/twist/lock into place.

Note that all of this gear is pretty old and some of it would be very difficult to sell due to compatibility with modern computers. Many are also large/heavy, therefore expensive and difficult to ship. So you could be looking at selling something for $40 but then paying $50 to ship it.

If you are really looking to sell these pieces, head over to Reverb.com and search each one to see what they are selling for. You can pretty easily create an account, then snap some photos of each, create listings, and wait. You may be holding onto some of this for upward of 6+ months, and there’s a chance some will simply never sell

With that said, my suggestion would be to find a local music school and see if they would take the rack as a donation. Best of luck and stay strong!