Dave and Anna have done a lot of good detective work here. The name seems to have puzzled transcribers as it 1901 it is transcribed as Neppers, so we have Neffers, Nippers and Neppers and perhaps elsewhere Nipper.
In 1901 Bertie age 19 is no longer shown as adopted but as son and is shown as born in Wales.
Living in the house are 3 Selby's plus a "nephew" Jim Nippers [transcribed as Sim Neppers]. This looks like a complicated extended family.
Anna is right, one should find Bertie, with much searching, as the son of a sister of James or Elizabeth or of a brother of James. "Adopted" children of this period usually kept their original surnames, by the way.