Refrigerators should be no larger than 6 cubic feet. With some help, I’ve estimated that the particular fridge in that photo is 24” tall, but there is quite a bit of space (probably > 30”) under those beds. Depth is limited by the width of a xl-twin bed (same width as twin). Width of anything under the bed is limited by the length of a xlong-twin bed (80”).

For the microwave, you should just get something small and inexpensive, I would imagine.