If you collaborate with other groups within the KB, there are some additional settings which can be used to define or describe your relationship with those groups. These settings are found in the SitePref tab under Group Relations.
See KB User's Guide - SitePref Tab - Managing Group Relationships for an overview of the group relationships.
Check the checkbox in the green Share Docs column for Unified KB Site (this should be the first row on the list).
From there, you can easily update the SiteAccess of multiple documents by using the Batch Update feature found on the Documents tab > Batch Update link. Enter the appropriate document ID number(s) and append/ completely modify your existing SiteAccess selections. More details can be found in KB User's Guide - Documents Tab - The Batch Update Tool
Check the checkbox in the blue Share iKB column for the KB Site with which you'd like to share your internal KB site documents. This will allow users who have internal access to that KB site to access your own internal site as well. Those users will still need to go to your KB Site to view these documents, though. Alternatively, you can edit each document you wish to share and add the new site as a sharing site.
For example, if the KB Admin for Site A were to check 'Share iKB' for Site B (as shown below) then any users with access to the internal KB for Site B would be able to go to Site A's internal site to view documentation. This can be helpful if two groups collaborate frequently and want to share internal documentation. Care should be taken to make sure that any sensitive content that Site B shouldn't be able to access is restricted using User Access Groups.
You first need to check the green Share Docs checkbox of the group with whom you want to share documentation. After this is done, you can edit the document in question, expand the Other Sites section, and check the boxes corresponding to that site. Should there be multiple documents that you want to share, you can easily update the SiteAccess of multiple documents by using the Batch Update feature found on the Documents tab > Batch Update link. Enter the appropriate document ID numbers and append/ completely modify your existing SiteAccess selections. More details can be found in KB User's Guide - Documents Tab - The Batch Update Tool
As noted above, you first need to check the green Share Docs checkbox for the group that you want to share documentation with in SitePref > Group Relations. If this is not done, these groups won't appear under 'Other Sites' when editing your KB doc.
If you check the red Trust Activation checkbox for the KB site in question, you will not be prompted to activate shared-in docs from that site. Instead, that doc will be immediately activated for your site anytime that site activates a doc that is shared with you.
By default, new KB documents that are shared with your site require approval before they will appear on your site. If you believe your approval is being bypassed for new docs, make sure that Trust Activation is unchecked for the site in question.