Switch on BLF when an extension is using an external line

I’m installing my first FreePBX machine; I have one sip trunk and two phones (Panasonic KX-UT133).
The extensions and the trunk are configured and I’m able to call with the phones via the external line.

Now I need to configure the phones so when one extension is using the external line the BLF button of the external line and the BLF of the extension is on on all the connected phones.
I have not found anything around so I’m asking if it’s possible.

In my tests the BLF buttons are configured with the number of the extension (1042 and 1043)

Thanks a lot

I managed to make it work more or less.
I have Phone A and Phone B.
When I make a call from phone A to an external number the led on phone B is off until the called number answers.
Is it possible to make it so the led on phone B is on as soon as I start calling from phone A?