Some details of the Redvers-Bate side: Manon Millington-Drake's parents seem to have been Reginald Redvers-Bate (1899-1967; perhaps the Reginald Charles Redvers-Bate b. London, s. of Albert Louis Frederick Bate; in the Gazette in 1919 and 1923 a 'Redvers Reginald Bate' was a Lt in the Royal Fusiliers, possibly the same individual? 'Redvers', given his father's surname of 'Bate' only, seems to have been used as a surname by Reginald's own choice [EDIT: see marriage notice below for indication that his father also used 'Redvers' as part of his surname after a certain point] and Mary ('Mollie') Francis (sic; 1898-1995) [death registered at Kingston upon Thames, Surrey], née Moseley, of Burracoppin, Western Australia. Her elder sister (b. 1925) was named Domini (married name Beiers; her husband appears to have been George Harold Beiers, architect, s. of Lt-Col Harold Mathieson Beiers [1889-1940], of the Australian Engineers, Australian Infantry Force in WWI). The Redvers-Bate family also lived at Crawley Avenue, with Mollie Redvers-Bate being a friend of the artist Elise Blumann according to 'Bauhaus on the Swan: Elise Blumann, an Émigré Artist in Modern Perth' by Sally Quin.
Person tags on the
trove.nla.gov.au site (newspapers, journals etc) suggest Manon to have been 'Manon Moseley Millington-Drake' and her sister 'Domini Moseley Beiers'; whether the 'Moseley' was a birth name or simply used to recognise their mother's family is unclear.
There is a 1923 marriage record at Marylebone for 'Mary F. Moseley' and 'Redvers R. Bate', indicating the above identifications to be correct; The Western Australian newspaper of 18 Nov. 1924 (on Trove) seems to show the Redvers-Bates arriving in Australia aboard the S.S. Gorgon, via Singapore. New Zealand Passenger lists at familysearch show the family (in 1935) using 'Bate Redvers' (unhyphenated).
Re: Albert Louis Frederick Bate (see above), an individual of that name (1862-) was a Colonel, R.A.M.C., C.M.G. (1915), trained at the Rotunda Hospital, Dublin (L.R.C.P.I., L.M. 1885), Commanding Officer of No. 4 Stationary Hospital, Woolwich at the start of the First World War, then at Le Havre. There is an 1897 marriage record at Natal, South Africa for an individual of this name and Emily Florence Wilson West (no parentage specified), presumably, given the dates involved, the mother of Reginald.
EDIT: Also from Trove, the following notice, from the Western Mail (Perth), 18 Oct. 1923:
'BATE - MOSELEY.- On August 27, at St James Church, Spanish-place, London, Reginald Redvers-Bate, son of Colonel Redvers-Bate, C.M.G., R.A.M.C., and Mrs Bate, of Sheerness, England, to Mary Francis (Mollie) Moseley, daughter of Mr and Mrs W. N. Moseley, of Perth.'
This seems to firmly identify the individuals concerned.