You mentioned a brother Ruben, there was a Reuben Mcallister born 2nd qtr 1912, transcription for his name is Rewirueben McAllister

Mother's maiden name Lowther.
He is on a number of electoral rolls in Lambeth during the forties, wife is Winifred.
There is a Henry McAllister/Mary Ann Lowther marriage in June qtr 1910 Greenwich.