Be aware, whenever you use the acid to brighten the teak, it eats out the softer grain of the timber, and weakens it by that much.
If you sand them, soon you'll sand them away.
With thin teak on that boat, I'd cause it to be wet down with sea water
daily, and leave it alone if you want it to stay there, and teach yourself that silver grey is a beautiful, natural color, God's will, like the natural color for bronze is green. In the case of your decks, if you don't sea water
and let it go natural, you'll be replacing it all the sooner.
Sorry to be the bearer of bad tidings.