Also re William Tennant Bain marriage to Lily Ward - how can I find if they had children & Lilys parents? (I'm not having much luck on Ancestry). 
Forget about Ancestry.
As it seems that they married in England, go to
https://www.freebmd.org.uk/search and search for births using surname Bain and mother's surname Ward. I just did and got 7 results. Then I searched for marriage of a male Bain to a female Ward and got 4. I've listed them chronologically, green for marriages, red for births
Battersea 1931
Elham 1931Elham 1932
Wandsworth 1933
Elham 1932
Dover 1937
Elham 1937
Hull 1941
Horncastle 1942
Woolwich 1948
Woolwich 1949
Woolwich 1953So looking at the dates and places I reckon that all but two of these births can be ascribed to one of other of the other couples (Battersea is next door to Wandsworth and it's too early to be WTB and LW's child anyway).
The remaining two are the one in Hull in 1941 and the one in Horncastle in 1942. They are far enough apart in time to be siblings, but both places are a long way from Dover. But it was wartime, so it's very possible that Lily was evacuated from Dover to somewhere safer to have her babies. On the other hand, the mother of the Elham babies could be the one who was evacuated. I can't think of any easy way to find out, short of sending off for copies of the birth certificates.
Digression - The William Bain and Lily I Bain in Portsmouth in the 1939 Register are not your William Tennant Bain and Lily Ward. Four reasons. First, that William Bain hasn't given a middle initial, though yours was almost always named with the initial anywhere else. Second, his date of birth is 22 December 1911, and we know from William Tennant Bain's birth certificate that he was born on 25 November 1910. Third, that William Bain is a stoker in the Royal Navy, but we know that your William Tennant Bain served in the Army, in the Royal Scots. Fourth, a William C Bain married a Lily I Restell in Portsmouth in 1935. Lily Irene Bain, born 7 November 1912, died in Portsmouth in 2004. This DoB matches the one in Portsmouth in the 1939 Register. William Charles Bain, DoB 29 [sic] December 1911, died in Portsmouth in 1999. So this couple is a complete red herring.
However I can't find William Tennant Bain, or Lily Bain née Ward, in the 1939 register. If he was a regular soldier before the war, they could have been stationed somewhere not in England ior Wales.
We know from the marriage notice that Lily's parents were Mr and Mrs A P Ward; that they lived in Dover; and that they were deceased by 1937. The marriage notice doesn't give her middle initial but it does give his. So I think we are looking for a plain Lily Ward.
The only birth of a plain Lily Ward in Kent between 1900 and 1921 was in Dover in 1911. According to the GRO web site the maiden surname of the mother of that Lily Ward was Menpes. An Irene May Ward, mother's surname Menpes, was born in Dover in 1909.
The 1911 census lists a family at 72 St James' Street, Dover consisting of Alfred Partridge Ward, wife Kate and four children including Irene, aged 1. Alfred and Kate had been married 10 years. And bingo! there is a marriage of Alred Partridge Ward to Kate Menpes in Dover in 1901. An Alfred P Ward, 39, died in Dover in 1913, and a Kate Ward, 52, died in Dover in 1929.
The only death of a Lily Bain born in 1911 that I have found was of a 93-year-old, born 16th April 1911, died in South-east Hampshire in September 2004.
So I think that Lily was born on 16 April 1911 in Dover, probably at 72 St James' Street, and her parents were Alfred Partridge Ward and Kate Menpes.
Does that help? You would, of course, need to confirm all that by getting all the relevant certificates. I could easily have got it all wrong!
