The Lewns don't make it easy. There is an Alice Lewn born to a Robert Lewn and Jane Clauge in Braddan on 26 June 1739, and also to a Robert Lewn and Margaret Christian on 25 July 1738.

The 1733 Will for a Margaret Lewn links well with the 1732 Robert Lewn Will on children's names. In your notes attached to the Margaret Lewn will, it says "sis christian;sis dau margt." If that is really "daughter in law Margaret Christian", then we have a solid link between these wills.