It can be done on a Mac and an iPhone, and it doesn't matter if members have an Android.
This group name is probably visible only on the Mac or iPhone, because it seems unlikely that one device could control how another device manages a group message. I haven't tested it on the other members of my groups so you can find that out with your own testing!
To set a group name on a Mac select the group in the conversations list on the left. Then click on the information button in the top right of the panel (the lower case i in the circle). This shows a panel with information about the conversation and you will see the option "Change group name and photo". Follow the prompts to edit as you wish and click Done. Then you will see the new name and images you edited in the list of conversations.
In iOS it's much the same, except instead of an information icon you touch on the picture and name at the head of the conversation. This shows the same options as I've described.