Betsey and Duncan Ross were in all probabilty illegitimate. There are transcripts of their baptisms on Freereg.
Betsey Ross born 10 Oct 1841, baptism 5 Dec 1841 Abode Tomintoul Father Donald Ross Mother Janet Cumming Natural child (this means Betsey was illegitimate).
Duncan Ross baptism 17 Oct 1844 Abode Tomintoul Father Donald Ross Mother Janet Cumming
The following is from a digest of the kirk session records for Kirkmichael. This is as transcribed
"Ron Donald 1841 Servant in Ruthven father of child by Janet Cumming".
Ron may be an incorrect transcription of Ross - there is a village called Ruthven in the parish of Cairnie, Aberdeenshire as well as a parish called Rathven in Banffshire.
The only way to see if these are your Duncan's parents is, as Monica has suggested, to download his marriage cert.from Scotland's People.
William