I too think of most Rangers as solitary, but there are times &/or circumstances when rangers would band together. You'd have to have a good storyline & reason for them to be doing so, as well as good challenging quests to play.
Think of Robin Hood & Sherwood ... not exactly rangers, but close to it. Men who took to the forest because their lands were getting pwned by the evil brother of the distant king.
Also, I can't help thinking of the streetguys I see wandering around with backpacks & shopping carts, etc. during the daylight hours right in urban America. Did you know that many of them sleep in communal campsites at night? Did you know many of them are Vietnam Vets who got stiffed by their own govt? (Ok, no politics) but you could make a guild of rangers who were war heroes who got rejected by their country for some reason ... and give them some purpose - revenge? getting back their good name? wealth? honor?
I don't know ... it's your Ranger Guild ......
