Yes, it is possible to group a pair of era 300 with a pair of era 100 for playing music.

However, if the Era 300s (or 100s) are being used as surrounds, you would need to remove them as surrounds and setup as a stereo pair, then group with the other Sonos room each time you wished to play music on just the 300s and 100s. You would then have to setup the respective speakers as surrounds again for movies. Note that each time you change room configuration, Trueplay is reset and you would have to run again if you currently use that option.

Thanks for the reply - 
Can i group the home theater(beam 2 + sub mini + 2 era 300) with a stereo pair of era 100 for both movies and music e.g spotify or sonos radio without having to manually modify every time the setup?

Grouping of rooms can be done with any room combination, on the fly. 
 

Be aware, though, that when watching movies there will be a 70msec delay in the sound to rooms other than the one with the home theatre setup. This is unavoidable and may cause a kind of echo if you have additional speakers in the same room. For me, I often have tv sound playing in the kitchen, but when I’m in there I can’t hear the other speakers, so it’s no problem. There is a position where I can hear both, but I simply don’t stand there!