Without individually setting the ringtone for each contact in that group.
Maybe there are other apps that manage contacts and have this feature.
Basically, I want my iPhone to ring the same when contacts from a group call.
You can assign ringtones to contact groups on iPhone using Grouptones tweak ($2.99 in Cydia, requires jailbreak).
See http://grouptonesapp.com for more details!
This is a feature that I want Apple to support, but hasn't yet. The "Group" mechanism in Contacts is a distribution list and only allows you to group contacts but has no editable meta information for you to change (for example, to change the default ringtone).
On an un-hacked iPhone, your only option is to edit individual contacts, and assign the new ringtone for each of them.
I have never hacked my iPhone, so there might be alternative methods available that I am not aware of. I will let someone else with a hacked iPhone answer that part.