As long as this baby is being fed properly, there should be no worry about MBD. Stay with the Esbilac mixed 1 powder to 2 water. How many times a day are you feeding?
This does not look like MBD to me. Just looking at her in the video she seems to be a wobbly normal 6+ week old. I have not done a physical exam so I am only going on the short video. Have you palpated her back legs to feel for any swelling or recent broken bones that may have already calcified? Something like that could cause her to be unsteady. I really think she is just young and a bit unsteady Yes, a little under weight. She will catch up in your good care.
She is darling.