Lets start off with some basics, since you started off trying to measure the microwave properties of the pin diodes with a DVM!
In your block diagram, to connect between the common port and the RF 1 port, you want to have -10 volts DC on bias pin 1, and you want perhaps 20 milliamps of current going into bias pin 2.
You show the length between the junction to the first pin diode as λ/4. That is close, but not quite exact. Because of various parasitics, and because of the phase shift thru the DC blocking capacitor, you probably want the length between junction and where the PIN diode is to be maybe 75 degrees at band center.
What pin diodes are you using. If they are packaged, they would have to be a microwave package (i.e. low package parasitics). Your via from top to bottom is good, but run at least two wires from top to bottom, or better yet mill a small slot and run a ribbon cable from top to bottom. You want the wire to be VERY SHORT! No extra wire loop at all!