For twitter, we do have admin access @wikicommons.
So, we should phrase also for @wikicommons
@wikicommons: Thank you so much @wellcomelibrary for your incredible donation of 100,000 images of medical history!
we should RT to disperse across our Twitter audiences, so we'll rt from @wikimedia, @wikipedia.
Back for the blog story,
I would tweak it to not have that awkward space between the twitter handle and the exclamation mark.
The @wellcomelibrary donates 100,000 medical images to @wikicommons -
bringing medical history to life for everyone!
from @wikimedia, @wikipedia
Then, since Fae was so instrumental in this momentous donation, we should thank her.
@wikicommons: Incredible work @Faewiki with @welcomelibrary - thank you so much!
RT from @wikimedia, @wikipedia
Facebook:
The Wellcome Library donates 100,000 medical images to Wikimedia Commons. The high resolution photographs and scans are used on Wikipedia to illustrate a wide range of topics -- such as disease, art history, cartoons, sexuality and biographies.
This looks fine to me.
Same for Twitter, we do have access to Wikimedia Commons so we should post the above there as well.
We could post also from G+ with the same copy, then reshare it.