Looking at my copy of Sussex Marriage Index for the marriages you mention above, there is a marriage
20 February 1655/6 at Denton Sussex for a Richard Elphick to Mary Swane 'of South Heighton';
and a marriage
29 May 1657 at Ticehurst for Richard Elphick to Elizabeth Pecknam.
The records for the 'marriage' of Richard Elphick to Elizabeth Willard is for "Banns only" in August 1656 at Brighton "Richard of Chiddingly" and "Elizabeth otsp", there is no record for a marriage.
Unfortunately the original registers for Chiddingly are not available to view on family search but, from the transcripts I have, there is no mention of a mother's name, the baptisms record either son or daughter of Richard Elphick.
Might I suggest that contact with the Sussex Family History Group via facebook may help to resolve the various Elphick families.