I have a new home and the floor joists are 2X8 and they are sistered and there is a bounce. There is hardwood on the floor when I'm sitting in a chair I can feel my 7 pound dog walk across the floor ( I can feel the vibration) Dosen't feel to strong Any suggestions

How long is the span? How far apart are the joists? Are there any braces installed between the joists?

I suggest you contact the local building department since they approved the drawings/plans and inspected your home for compliance with same. You can also obtain a copy of the drawings that were approved for a very nominal fee from the building department. Naturally I suggest you obtain the copy of the exact plans that were approved for your home since if the building inspector missed code compliance on the original plans or did not inspect your home properly once they find out the plans could get lost if you know what I mean. I have seen that happen before.

2x8 are really not sufficient for floor joists. I think you're in trouble.