I have two rooms next to each other and I'm going to put a Sonos Beam (Gen2 ) in each of those rooms. Each soundbar will be connected to a tv.1.Is it possible to pair the two soundbars and listen to the same music?2.Can I hear what one of the televisions gives on both soundbar at the same time?3.Putting the TV in mute mode, can I listen to music from the app and the TV broadcast continues to play?

1 Yes. Not “pair” in Sonos terminology, but “grouped”. Speakers/rooms can be grouped to play the same music. 
2 Yes, but… In order to play sounds in sync to multiple rooms, Sonos has a slight delay at the start of the streaming signal. For music, this doesn’t really matter: do you notice it takes an extra 75msec for the music to start playing? But for a TV signal, the delay to the connected Beam (or other home theatre product) is minimised to reduce any lip-sync issues. Any speakers grouped to that Beam will have the delay. If you are in a location where you can hear both speakers you get an odd echo effect. 
3 Most TV’s need to be set into a “use external speakers” mode in their settings. You could therefore switch back to “use internal speakers” and stream music to the Beam. I think that’s what you’re trying to achieve? Or, don’t turn off the tv but start streaming music to that Beam - it doesn’t care what you’re asking it to play. 

For example I'm watching a concert on you tube, will I have the echo effect?(being music playing)

For example I'm watching a concert on you tube, will I have the echo effect?(being music playing)

You will get an echo whenever the source is the TV. You can probably get an acceptable  sync by adjusting tbe TV sync delay setting for one of the Beams. This will be at the expense of audio-video sync, but that might not matter here.

For example I'm watching a concert on you tube, will I have the echo effect?(being music playing)

It’s the source of the signal rather than the type or content of the signal. If it’s a tv/video source through the HDMI input, assume the delay to other rooms/speakers will be introduced.