Stephen Hollis 25 Arobelle Hollis 33 Lewis H Abbott 7 Chesley W Hollis 5/12
The index for 1850 census is incorrect. It calls Lewis "Lewis H Hollis" but when you look at the actual record, he is enumerated as Lewis H Abbott. It appears that Arobelle was married to an Abbott first and then to Stephen Hollis. This is supported by the age difference between Stephen and Arobelle and the gap between Lewis and their child Chesley. Also it is unlikely that Stephen would have had a child at age 18. In any case, Lewis would not have had a different name.
The only other explanation is that Lewis was "taken in" by Arobella an older sibling, but I think just at first glance that Lewis was Arobelle's son. It is important to find a marriage record between Stephen Hollis and Arobelle Lewis around the Kingfield area and determine if it was her second marriage.