node/[group nid] - the group start page, with timeline / activity stream.
node/[group nid]/about - group description, location info, etc.
node/[group nid]/events - list of group events
node/[group nid]/forum - list of group discussions
The */events and */forum might be implemented as panel variants, views pages with node argument, or as custom hook_menu() items.
On e.g. a group event node/123, you want a breadcrumb like this:
Home » Groups » Group 55 » Events » Event 123
^ /groups (views)
Build-in plugins shipped with Crumbs
Crumbs already has built-in plugins for Organic Groups.
When enabled, these can get you this far:
Home » Group 55 » Event 123
This is already quite ok, but we want more!
On Admin > Structure > Crumbs > Entity parent > Node:
On node type "Group event", type
for the parent path.
On node type "Group", type
for the parent path. (if this is the path of the view to list all groups)
This may already be sufficient.
If not, you may need to give the crumbs.entityParent.* plugins a stronger priority.
Visit the page with your group event (node/123). Have a look at the breadcrumb.
The breadcrumb does not work yet?
Visit Admin > Structure > Crumbs > Debug.
Type node/123 in the text field, and click "Go".
Now you should see the different plugins in action.
The interesting one is
If this is not active, you may want to give it a stronger weight.
On Admin > Structure > Crumbs > Plugin weights:
Move the "crumbs.entityParent.* into the "Enabled" section, and move it far enough up.