I wouldn't recommend this.. When you plant in the same pots. Plants tend to try to choke eachother out. Their root system will sprall as far as it is able to. Crossing paths with other roots from the other 2 plants choking one another.
Secondly.. An aquarium is glass and will allow light to shine on the roots around the outside edges of the aquarium. Roots dont like light and will die off in those areas. This will stunt your plants and/or kill them.
Good luck.
You could do that I guess. And maybe paint the outside walls black. However, what would you do about drainage? Could you drill holes in the bottom of the aquarium? It just seems so much more economical to get 3 seperate pots.