I currently own a 2.5T stinger and in the future the main modification I was thinking about was if it was possible to add another Turbo and the difficulties along with doing so.
Ok I'll be nice and give you a serious answer: this would almost certainly be a ton more trouble than it's worth. A far easier path would be to either sell it and buy one that's already twin turbo, or stick to a single turbo upgrade that will be much less complicated.
I assume you're talking about a sequential setup, and even cars that came with those from the factory (Mazda, Supra) are usually converted to single turbo when modified, for simplicity.