You don't say how far apart your posts are for the beam, or size. Is it southern yellow pine for joists? Is the 2x10 ledger, bolted to a 2x8 rim joist?

That is a lot of weight hanging, especially if you're not bolted through the ledger, and not hitting floor joists. You need a lot of shear strength, which the architect should have spec'd out.

I'm surprised solid blocking or cross bracing isn't specified on the plans.

9 feet apart are the 6x6 posts sitting on 10 foot deep 12" piles. Ledger is lagged to the rim plate which is 12" thick cement with steel plates that were set into the cement on the ICF pour every 16" as per code.
On a side note I put in blocking today at the 4 and 10 foot mark going out from the house on the 14 foot joist run to the beam plus 2 foot overhang = 16' run and did not seem to help in the bounce.

Just shooting from the hip here, and without looking it up, I do believe your posts are too far apart.

The architect should have the load calculations on the plan. It certainly seems to me, the dead load is way too much.

You can search online for a load calculator, and figure out the dead load. Its been a long time since I've built one, and things change, but I believe you're supposed to be around 10# per square foot for the dead load.

BTW, 10 foot deep on the posts? Where is this?

In Canada. Water table made the screw pile installer and engineer go down that far. Also with the tech lamaminated 3 ply beam 2x10. ( It took a small crane to lift) they were told they were in overkill mode. Which I tend to build like. I was the builder not the engineer in this. I showed up and the piles and posts were up from the builder, then I took over. I agree I never would of built it with only 3 posts span. The homeowner wants the underneath patio area post free. Next up sistering another 2x10 to each joist. I wonder if I can just screw the joists to the existing ones. Probably cut them a couple of inches shorter for ease of getting them in.

If you sister to the existing joists, you're adding to the dead load. Something you do not want.

So the other option I have is to put in a joist between each 16 as it sits now. Does that help the situation

How high is this? Do you have a picture you can upload?

I wouldn't say that's your only option, but I'm not an engineer by no means. (I still believe the posts are too far apart)

Possibly diagonal bracing down to the posts from joists, may be another option.

Approx. 10 feet off the ground. With double french doors on the walk out onto the lower patio area.Below this deck.

Search images on Google for, Deck Bracing. You probably want to search Deck Failure, as well.

Last thing you want is a failure. It really doesn't matter if the customer wants less of this or that. It has to be safe.