Basically yes. The signal is reproduced without delay on all speakers, which is not dependent on the signal source. I have never tried this with line in, only via Bluetooth.

We have received the following information from a customer:

Hey, not true:
A) slight delay for bluetooth and line-in during playback.
B) Re-streaming of the AUX signal is not (yet) possible.

yes, the systems can be interconnected via the mobile app (without delay).
Make sure you have a good WIFI connection!