twin turbo question

So ive only ever dealt with single turbo set up cars, and when the turbo makes says 10psi thats what the motor gets. But say you have small twins so you arent waiting on lag and each is set to 8 psi. We will say they are the same size, non sequential. Just true twins in parralel. Does it stay as 8psi of boost, or since there are 2 does it double to 16? Or am i wrong all together and some how end up with 12psi? Ive wondered this for awhile, as i said ive never dealt with twins and it just seems in engines that only rev to 5k twins that boost at 2k are better off than single that starts at 3k+? Thanks for any input. :newb: