The bottom does look like a double barrel so I would say yes it's probably 8 inches high with a seperator in the middle. The top tier I'm not sure of the height but I would say there is a diameter difference of 3-4 inches between the top and bottom tier.
Thanks so much for the insight!!
Yes it does look like a 4" difference between the top and bottom cakes. I would say go with 4" and 8" cakes.