As long as they are both using the same OS (S1 or S2), you should be able to group them. Assuming you’ve  set them up in the same Sonos ‘household’, using the ‘add a device’ function in the controller. 

It’s not uncommon for folk to accidentally create 2 systems when trying to add speakers, so they can only see 1 set of speakers at a time. If you’ve done that try factory resetting one set of speakers and then “add to existing system”.