Two pressure tanks will not raise pressure or solve any type of pressure problem.
It will prevent the well pump from coming on so frequently but... you'll be pumping more water out of the well all at once than with just the one tank.
Your problem is either partial blockage in the line going upstairs or the pressure switch settings for your pump or the pump you have may be undersized or worn out or have a partial block in the jet etc.. Or the level of water in the well is less than it used to be and the pump can't keep up.
Do you have a jet pump, one or two line, or a submersible?
What pressure switch settings are you running it at?
When was the last time you checked the captive air pressure setting in the tank?