As you have mentioned, currrently PS.com users do not have access to change/modify tags & descriptions for other owner's images. As you have mentioned the images you have uploaded/added in Group Album are all owned by you then collaborators will not have rights to modify the tag & description of same.
But you can give your login info of PS.com to your family members and then they will be able to assign tags to the images in a Group Album or other wise.
You can find generic help around Group Album @http://help.adobe.com/en_US/Photoshop.com/Using/WS58a04a822e3e5010-7314c3b112642d98cdb-800 0.html but the specific case which you have mentioned is not added there.
Thanks for raising this question, we will add it in our help as well as in FAQ.
Let me know if this helps.
Thanks for the response... I now know that I have not missed something.
As feedback for you... I really like the concepts included with the synching
and creating albums based on tags. My sense is that my usage scenarios must
not be quite what the designers/product managers designed the capabilities
for. My scenario is not so much the creation of beautiful images as it is
managing a very large effort of making a family image collection useful and
available in interesting ways to many family members. In our case the
photos go back to early 1900 and it takes a real collaborative effort to get
them identified and tagged... I suspect there are many (perhaps most) other
families who have a need/desire/potential to do the same. In my case , I
would have initiated some dozens of new users if the capabilities were
there... Clearly the product needs some minor tweeks to make it really great
for this purpose. Even more so, you need some tutorials,
documentation...help for the floundering user... this is a real issue. I
have spent several weeks almost non-stop getting to where I am... and at
this point I must say I am questioning my choice of tools... mostly because
of how difficult the journey to here has been. Hope these comments are
Again thanks so much for responding... it will keep me going!