2 bottles of spary?

yes you can use a y piece no problem.

You find running 1 bottle is better, it will allow you to use more on the N2O at a good pressure instead on bringing them both down.

Never run them empty and never over fill them. When you get down to a few pounds you start to suck more air then N2O. 950psi is a good start...

You can do that, but as soon as both bottles are on line, the pressures in the bottles will equalize. If the bottle heater has one warmer than the other, it will drop some, and the cool bottle pressure will rise, until they are the same. If the temps are close, it should work ok.

If you make sure you open both bottles and allow them to equalize before you run, it should work. If you do it at the last minute, you may loose more pressure while the highest pressure bottle is flowing into the other bottle, vice all of the stuff flowing to the jets.

If both bottles are at the same, you would have at least the same flow as one, and a bit less pressure drop during a run.