I would recommending getting hold of the wills of William Bentley (d. 1880, possible father) and Hannah Bentley d. 1897. The people to whom probate was granted are not necessarily the same as the beneficiaries of the wills, and Emma, George, or both may be mentioned.
Sometimes, 'natural' children are made specific reference to in wills. Or he may be listed as 'adopted' - there wasn't government-regulated adoption as we think of it but unofficial adoption was not uncommon, and it seems that the Bentley's cared for him over a long period of time + possibly left him an inheritance.
You can search for wills/probates and order online:
https://www.gov.uk/search-will-probate(note: if an entry says 'administration' granted there was no will and ordering the full record will not provide much info - if it says 'probate' granted there's a will and you can get a copy of it).
It would also be worthwhile getting the birth certificate of George - the "Seeley" entry mentioned upthread seems to be him. Possibly that will give you a better idea to Emma's middle name(s)? It might also confirm if she was living with the Bentley's at the time, or if not where she was resident.
