By Default systems are initialized by the Aircraft/generic/generic-system.xml
This initializes the following:
- The generic electrical system
- 1 pitot system, index [0]
- 1 static system index [0]
- 2 vacuum systems [0] and [1], depending on engine rpm of engine[0] and
  engine[1] respectfully

If you want to define more systems, copy the generic-system file to your
aircraft-name/Systems folder and rename it systems.xml

In your aircraft -set file add the path to the system.xml file:
<sim>
    ....
    <systems>
        ....
        <path>Aircraft/aircraft-name/Systems/systems.xml</path>
        ....
    </systems> 
    ....
</sim>


** Adding a second pitot system.
In your systems.xml, you should already have

  <pitot>
    <name>pitot</name>
    <number>0</number>
  </pitot>

and you need to add for a pitot system with index 1:

  <pitot>
    <name>pitot</name>
    <number>1</number>
  </pitot>

For the any pitot system except for the first (with index 0) 
add in the aircraft -set file (below for index 1):

<systems>
      <pitot n="1">
                <serviceable>1</serviceable>
      </pitot>
</systems>

Of course you can add a third or fourth etc.


** Adding a second static system
Absolutely analog with the pitot system. So add in systems.xml:

  <static>
    <name>static</name>
    <number>1</number>
    <tau>1</tau>
  </static>

and in the aircraft -set file:

<systems>
      <static n="1">
                <serviceable>1</serviceable>
      </static>
</systems> 

Now you can source your instrumentation relying on static and pitot
pressure (airspeed, altimeter, vertical speed indicator) from different 
and independent systems