Hello
Pressure is not a problem, as it will equalize anywhere in a system as long as the hose is of sufficient diameter. What I mean is, if you connected 10 poles to a 60PSI pump, (neglecting any resistance in the pipe) you'd find they all were delivering water at 60 psi.
Its FLOW RATE that will be affected. If your maximum flow rate is 4 Litres per minute, and you connect 2 poles, it will deliver at 2 litres per minute each. Also, something to bear in mind is that when using 2 poles with one system, if one pole is extended 30 ft up and the other is doing the ground floor, the distribution of water will not be even, you'll have more flow on the lower pole, as the water isn't having to "climb" a height. Easily overcome this by both working at the same height at the same time.
-Philip