Hi @palmos, welcome to the forum! 
QGC listens for mavlink messages on port 14550, so in your script you should be able to use pymavlink to connect to and send messages to QGC, as covered in the “Read & Send Script” subsection of this post. You can test the connection with a message like
master.mav.statustext_send(mavutil.mavlink.MAV_SEVERITY_NOTICE, "Qgc will read this".encode())
which QGC should read out loud when it arrives.
Understandably you’ll need to be using the relevant gps and depth messages instead of the named_value_float message I was using in that post, and there’s a section called “Send GPS Position” towards the bottom of the pymavlink page I linked to above
For the depth message, you can look in the mavlink common message set to find the appropriate message to send