I found the list for the immigration to Boston in 1848, and Samuel is not on it, but a Sarah Harris is, so is she a sister to Samuel?or a sister-in-law?
they were on a "Brig" named the Lady Campbell.
Could Samuel have been married before? and widowed? he is a bit older than Eliza, there is a Sarah Harris born 1815 daughter of Samuel and Grace at Bideford. or she could be the wife of a brother to Samuel. I expect Samuel went ahead to Ohio and sent for the family once he had found work etc.
Perhaps they went off soon after George was born, and did not register him, I have been looking on 1841 census and cant find them. If they had been here they would all have been on, as the census that year was in June, and if his birth in April that year is correct, which seems to be right, he would have been a few months old.
They also seem to have been nonconformist/methodist/Weslyan, which is not good records wise, as their records are a bit hit and miss!!I had Baptist ancestors to trace, and am pretty certain where they were buried, but no stones and records not as organised as the CofE!!
They were all very brave in those days, I have been working on a family line where my great grandfathers brother aged 17, went to Australia, and further back their aunt and husband went in 1855,
they are listed as pioneers in Australia, so am now thinking their nephew must have heard about them, perhaps family were in contact, and he went to join them? So now we have family in Australia as well as Canada!! (My great uncle went out there aged 16)

Will keep my eyes open and if I spot anything will let you know.