I have no experience with this, but my mind is rolling and I think this would be pretty cool. First question, what is the tank material? Acrylic or glass (most likely)? Second question, how good are your tank drilling skills and are you any handy when it comes to plumbing? I'm thinking build a stand or find a stand that fits both tanks, and drill out the side for both tanks with the same size hole and then attach them with PVC
pipe (clear if you can find it) and use some fitting and aquarium safe silicone to attach them. If you can do it, your tank(s) will look awesome! TBH however, I'd be a little afraid and nervous of doing it myself.