Hi Debbie,
FamilySearch has a marriage on 21 Apr 1720 at Croglin of John SLACK to Deborak MULCASTER. There are four children of John & Deborah SLACK recorded on FamilySearch as baptised at Huddlesceugh/Parkhead Meeting House: Sarah 17 Jan 1722, Anne 26 Mar 1724, Jane 03 Oct 1725 and Robert 24 Apr 1735.
You can look up those baptisms in the Huddlesceugh Register on Ancestry as they may give a clue as to where the family lived at the time. Worth looking up the marriage while you are at Carlisle RO.
I also managed to find a marriage of a Mary MUNCASTER (presumably a variant of MULCASTER) to a Ralph DOBSON on 10 Jan 1733 at Kirkby Thore, WES.
There was a baptism on 29 Nov 1696 at Croglin of a Deborah MULCASTER, daughter of Thomas [edited due to previous typo]. There was also a baptism on 07 Feb 1708 at Huddlesceugh of a Mary MULCASTER, but no parents named on FamilySearch.
MUNCASTER/MULCASTER is a rare name, so that should help, if this is indeed the right family.