The info about 10 mg was posted on metzer - it was mentioned in the article as well, but the dosage that was given is different than what metzer recommends.
https://www.metzerfarms.com/blog/are-my-ducklings-leg-problems-due.html
Take a look at this thread with the same issue:
https://www.backyardchickens.com/threads/pekin-duck-walking-on-hocks.1047634/post-16046843
This was after visiting the vet:
https://www.backyardchickens.com/threads/pekin-duck-walking-on-hocks.1047634/post-16094016
What feed are they on?
It looks like the one has learned to walk on her hock.
The other one is slower than most ducklings, but maybe its compensating for its friend.
The recommended dose of the super b complex is 10mg.
@Miss Lydia