Did you manage to sort this?
My grandfather was Frederick Minter Thomson, born 1887 of John Minter Thomson (merchant seaman, b 1851 Scotland) and Sarah Jane Northmore (quarryman's daughter, b 1853/4 Plymouth) m 24/3/1872
He was boarding with Phoebe Dennis in 1891 and adopted by her at 1901 Census.
He had 3 sisters, Ethel (b 1881 Plymouth), Lily (b 1885 Plymouth) and Hilda (b 1891 Plymouth)
Often wondered what happened to John and Sarah, since I can't find a trace of them