Never used the stand, but I took a look at Amazon and found somebody asked the very same question:
https://www.amazon.com/d/Aquarium-Stands/Imagitarium-Newport-Gallon-Wooden-Stand/B008VRXDTO
I will copy and paste it for you -
"Can this hold two tanks? A 20g high on the top and a 10g on the lowest shelf? I would take off the middle one or not attach it"
Answer 1: "This is a well built stand and is very sturdy so I don't see why not. I probably would not put it on the middle shelf but the top and bottom shelves should not be a problem."
Answer 2: "Your plan would work for the two tank fit but I think this Stand needs that middle shelf for support strength. It's a beautiful Stand and I'm not sorry I got it. But it is tippy, VERY tippy. I have only a 10 gal sitting on the top."
I would take a look at the reviews and questions section there, tons of info unless somebody here has firsthand experience with it!