Hi Goldie,
Tom's chart gives no details about Margaret Davies's parents, but her marriage record [1803] has one witness as "John Davies". The IGI shows 4 children of Thomas Davies and Cath Cashin as John [b.1777], Catherine [1779], Margt [1781], Jane [1795].- So it does indeed look likely that they were sisters. Perhaps a will/admin would confirm this? Brian Lawson's website has an entry for DAVIS, Thomas 1818 Mau E 2, film number: 0106419.
Sue