Hi, I found the family on the 1851 census, which i am guessing you have as you have details about Margaret, this looks like them on the 1861. As Joseph and Janet have died after 1855 you will be able to get their death records from scotlands people which should give you their parents names. Tracing them in the census's should narrow down their years of death.
This is the 1861 census i found, if you need any more just let me know,
Joseph RUTHERFORD 38 head ploughman brn halfmorton Dumfries
Janet 36 wife agr labourer brn Cummertrees, Dumfries
Margaret 10 daught brn Anan
Jemima 8 daught brn Anan
Andrew 6 son brn Cummertree, Dumfries
William 4 son brn Cummertrees, Dumfries
Joseph 1 son brn Anan
They were living at Howes Cottages , Anan
Reg Number 812/ED8/Line 24
Susan