Try this:
gst-launch-0.10 -e -v souphttpsrc location=“http://194.168.163.96/axis-cgi/mjpg/video.cgi?resolution=320x240” timeout=5 do-timestamp=true is-live=true ! jpegparse ! jpegdec ! nv_omx_hdmi_videosink overlay-x=500 overlay-y=500 overlay-w= 500 overlay-h=500
You will need to create similar pipelines for other 3 streams and run them concurrently after tweaking the overlay-* parameters as you want.
Let me know if this helps.