Ardupilot installation problem

hi i have used following links to install ardupilot:
http://ardupilot.org/dev/docs/setting-up-sitl-on-linux.html#setting-up-sitl-on-linux

following is the error when i try to make jsbsim

Makefile:487: recipe for target ‘libInit_la-FGSimplexTrim.lo’ failed
make[2]: *** [libInit_la-FGSimplexTrim.lo] Error 1
make[2]: Leaving directory ‘/opt/jsbsim/src/initialization’
Makefile:612: recipe for target ‘all-recursive’ failed
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory ‘/opt/jsbsim/src’
Makefile:387: recipe for target ‘all-recursive’ failed
make: *** [all-recursive] Error 1

Moreover when i try to run sim_vehicle.py i get following error:
Traceback (most recent call last):
File “…/Tools/autotest/sim_vehicle.py”, line 25, in
from pymavlink import mavextra
ImportError: No module named pymavlink

i have upgraded both mavproxy and pymavlink again and again but it gives me same thing
Requirement already up-to-date: pymavlink in /home/muntaha/.local/lib/python2.7/site-packages (2.3.7)
Requirement already up-to-date: MAVProxy in /home/muntaha/.local/lib/python2.7/site-packages (1.8.8)
Requirement already satisfied, skipping upgrade: future in /home/muntaha/.local/lib/python2.7/site-packages (from pymavlink) (0.17.1)
Requirement already satisfied, skipping upgrade: lxml in /home/muntaha/.local/lib/python2.7/site-packages (from pymavlink) (4.3.5)
Requirement already satisfied, skipping upgrade: pyserial>=3.0 in /home/muntaha/.local/lib/python2.7/site-packages (from MAVProxy) (3.4)

kindly tell me exactly how to solve these issues
I want to install ardupilot on ubuntu xenial

i also have three versions of python ins my system kindly tell me how to make python 3.6 default to be used for ardupilot? is it right to do or not?

The instructions on this page are outdated, Ardupilot now works with the latest JSBSim master.
For using JSBSim, see the following page - http://ardupilot.org/dev/docs/sitl-with-jsbsim.html

Regrading the pymavlink issue, not very sure what’s going on.
Did you use the install-prereqs-ubuntu.sh script to setup the environment?
pip defaults to python3 now so that might have caused some problem

According to me, it’s better to stick with Python2 for ardupilot since everything works correctly with that (someone else could provide detailed info on python 2 vs 3 for ardupilot)

Hope this helps

ok then i will delete the python 3 version and stick to python 2 and yes i used that script the script run successfully
thank you i will use jsbsim master and will get back to you
one more question i am installing ardupilot and jsb in same directory /opt is it ok?

i run jsbsim commands completely
i installed ardupilot and jsbsim in root directory
but still i am getting this error:
Traceback (most recent call last):
File “/ardupilot/Tools/autotest/sim_vehicle.py”, line 25, in
from pymavlink import mavextra
ImportError: No module named pymavlink

i also removed python 3
kindly help me how to solve this issue