The guy on the left is frozen (suspended animation),
The next one is a hybrid 1/2 sectioid 1/2 human. He was going to be scaled up in code to make him nearer human size.
I think the red one is a commander ( there was a High Mentat class as well so it could be one of them, but I seem to remember that they were in a flying chair like the Mekon.)
The last one is a standard Grey. They have caste marks on their foreheads.