Can a gas giant have an other gas planet as satellite? Is it possible for a gas giant (A very big one) to have an other smaller gas planet as satellite?
It would seem so.

Think about brown dwarfs. At the lower end of the mass spectrum, they're only a couple dozen times that mass of Jupiter, and only a couple times the mass of Hot Jupiters. Some brown dwarfs have been found to have planets. Taking a look at some examples:


2M1207: Roughly 25 Jupiter masses, this brown dwarf has a planetary-mass object orbiting it, 2M1207b. This object has between 3 and 10 times that mass of Jupiter, and is fairly hot, although it orbits far from the star.
2MASS J04414489+2301513: Roughly 20 Jupiter masses, with a companion on the scale of 5 to 10 Jupiter masses that could be a planet.


Note that these brown dwarfs are very low-mass, only a bit more massive than hot Jupiters. They can have orbiting gas giants - why couldn't high-mass hot Jupiters have the same?