Hi
I'm afraid that I can't see a Martha Newland - Martin marriage on the Sussex Marriage Index.
But assuming that Martha was a widow, as stated in the marriage register, at the moment there is only one way I can see what might(!) have happened.
It would mean that Martha would have been widowed twice, not impossible of course, but more complicated. Sorry it's so long, it helped me make sense of it, it may give you something to consider. Hope you can see the links to FamilySearch, you need to be logged in as a free member.
It starts in Heyshott, near to the places previously mentioned
A baptism, 29 March 1778, Martha, daughter of John + Martha Carver
https://www.familysearch.org/ark:/61903/3:1:S3HT-DY29-DHC?i=473Marriage at Heyshott, 15 July 1798
Thomas Williams + Martha Carver (who marked)
https://www.familysearch.org/ark:/61903/3:1:S3HT-DY29-C2D?i=497There is a baptism at West Dean, 12 January 1800, Mary Ann Williams, parents Thomas + Martha
Bishop's Transcript here
https://www.familysearch.org/ark:/61903/3:1:S3HT-D179-BVZ?i=1064&cat=67529 On the next image of the West Dean BTs (im 1066), a burial of a Thomas Williams, 16 Feb 1800.
No further Thomas - Martha Williams baptisms in Sussex are indexed on FamilySearch, so could that be Martha's husband??
A marriage at Easebourne, 24 May 1802
William Martin
+
Martha Williams, widow (marked)
https://www.familysearch.org/ark:/61903/3:1:S3HT-D1L9-WQL?i=286&cat=144653Seems to be no baptisms to that couple there, but back at Heyshott, there are two
burials in 1804
PR image very poor
BT not great!
15 February 1804, Martha, daughter of William + Martha Martin
23 April 1804, William Martin
https://www.familysearch.org/ark:/61903/3:1:S3HT-D1S9-1LC?i=482What do we have for this William Martin?
Well possibly he is the chap baptized at Heyshott, 4 August 1782, parents William + Elisabeth Martin.
According to the index on FamilySearch those parents may have married the next day??
The older William Martin may have died in 1834, buried in Heyshott on 19 April, age 83.
So if that was the younger William's burial in 1804, it would leave a widowed Martha about who might have married Francis Edwin the following year.
A fly in the ointment might be a baptism of a Henry Martin in East Grinstead in 1807, the only other William/Martha Martin baptism in Sussex indexed on FamilySearch. Grinstead is further away though.
plus
Francis + Martha Edwin also had a Mary, baptized 31 July 1808, at East Dean.
On the other hand the baptism of Martha Carver in 1778 ties in with the death reg of Martha Edwin in 1848, age 70.
