You need an engineer or a very skilled contractor who know where to go for information. There is no easy answer over the internet for your situation. Your questions prove your way over your head in my opinion.

What is the spacing of the joists and how deep are they?

9.5" tall (so I guess in building that's considered 10") and 16" on center. thanks.

Are you sure the bounce is coming from the joists? it could be your subfloor is not that secure to the joists.

Im not an engineer (have a degree in it, but not professionally qualified to give advice) so you still may want to seek out that advice.

But what im suggesting, is see if you can see any noticeable sag in the joists, and then also try screwing the subfloor off in a "bouncy" area, and see if that works.

Gregmills,
thanks for answering.I'll def get a pros input. Anytime anyone walks, even when our 100 pound dog runs through the kitchen, you can feel the bounce.

The house is only 14 years old- we have been in it for 6 years, and it's always been bouncy, doesn't look like it's sagging, just very bouncy in my opinion.

thanks again.