No, I don't know Marjorie's middle name, all the information that I have has been obtained without access to certificates and, obviously, I'd have to get copies of them to absolutely confirm what I believe to be:
This is the chronology as I see it. I have more data on William but no further information about Mary or Marjorie.
Mary Ann GREEN b Dec 1878 Abergavenny, Monmouthshire - Abergavenny 11a 71. Parents George and Jane b 1858.
1881 Census aged 2 living at home
1901 living at home, aged 22. Siblings Louisa, Thomas, Alice.
1915, September married William MEAD Paddington 1a 75. (Married at William's home?)
1916, December Marjorie S MEAD born Salisbury 5a 245.
1917, December William Thomas MEAD dies.
1932, March Mary A MEAD d. aged 55 (born 1877/78) Devizes 5a 139.
No further trace of Marjorie as yet.