Hi I've just had a quick look through my Devon Salway/Solway/Selway records and have no connection.Following them on census it would appear that Francis Salway was the son of William and Hannah, and was born in Ubley, Somerset c 1825.Ubley is not on the IGI so you need to search the parish registers.He seems to have had a sibling named Alfred with whom he appears in the 1841 census up in Cheshire. I haven't found a marriage to Emma but I have only looked briefly on FreeBMD.William Salway was also of Somerset, not Devon.
In 1841 Emma is 19, a servant, in Sutton.In 1851 she appears in Dorset as an unmarried servant with a Jane Gill half her age.By 1861 she has married Francis Salway/Selway.
It would appear that Rebecca and Caroline are grandchildren of Richard and Lucy Gill (1851). James Gill appears as son of Richard and Lucy in 1851 but as son of Emma in 1871. In 1861 is is a brother in law of Francis. Jane Gill appears as daughter of Richard and Lucy in 1861 and in 1841.
Since both Caroline and Rebecca were born c 1843 and 1846 it would appear that they were illegitimate and probably not children of Francis.You really need to refer to the parish registers to confirm their parentage.
Here are the census details in case you don't already have them:
1871 No 17 Copenhagen St, Portsea, Hampshire Francis Selway head mar 47 labourer factory born Somerset Ubley Emma wife mar 50 Dorset Sutton Rebecca Gill dau unm 24 general servant/domestic/unemployed Sutton James Gill son unm 35 labourer general Sutton
1861 Lower Lane, Portland, Dorset, Francis Selway head mar 35 railway laborer Somerset, Bristol Emma wife mar 39 Dorset Sutton Rebecca Selway dau 14 Sutton Louisa Gill niece 2 Sutton James Gill brother in law unm 28 railway laborer Sutton
1851 Winterborne Came, Dorset Emma Gill servant unm 30 servant Sutton Dorset Jane Gill servant un 14 servant Sutton Dorset
1851 Preston, Dorset Richard Gill head mar 61 labourer Sutton Lucy Gill wife 50 Sutton James A son 18 labourer Sutton Caroline granddau 8 Sutton Rebecca 5 Sutton
1851 Tintwistle, Cheshire Francis Selway lodger unm 26 labourer Somerset Bristol Alfred Selway lodger unm 24 labourer Somerst Bristol
1841 Compton Martin, Somerset Francis Salway 15 MS bic
1841 Compton Martin, Somerset William Salway 47 ag lab bic Hannah 42 bic Elisha 22 bic Alfred 15 bic Joseph 1month bic Mary 13 bic Jane 6 bic
1851 Compton Martin William Selway head mar 50 ag lab Somerset Stoke Lane Hannah wife mar 53? Ubley Jane dau unm 16 ag outdoor serv Ubley Joseph son 10 scholar Compton Martin
1861 Preston, Dorset Richard Gill head mar 71 Pauper Sutton Lucy Gill wife mar 65 pauper Sutton Jane Gill dau un 24 laundress Sutton Caroline Gill dau unm 18 Tailoress Sutton
1841 Sutton Richard Gill 45 ag lab bic Lucy 40 bic Levi 15 bid James 15 bic Mary 10 bic James 8 bic Jane 4 bic HO 107/285/15/9/12