Secondary sources give them a son, Harwood CURD, who married Hannah PRICE, but no such son is mentioned in Edward's will.  Did Harwood die without issue, before his father wrote his will?

Some secondary sources give Elizabeth's husband as Cuthbert WILLIAMSON, not Richard WILLIAMS.  I don't know which is correct, but as her father calls her "Elizabeth Williams" in his will, it will take strong primary documentation to prove she married a WILLIAMSON. 

1.  Messages in the Curd Family Genealogy Forum (online at GenForum.com).  In particular, Messaage #76, in which "Barbara Jean" cites the following:

1a.  Benjamin B. Weisiger III.  c1976/7.  Colonial Wills of Henrico County, Virginia.  Self-published, Richmond, VA (repub. 1995 by Iberian Publ. Co., Athens, GA).

Page 1177 WILL OF EDWARD CURD Executors: wife Elizabeth and son Edward To wife for life, any dwelling house and all belongings and land, only [meaning "except"] son Edward to have half, and after wife's death, all of it; also negroes to both. To son Edward, all my land in Goochland County. To son John, 2 negroes. To son Richard, 2 negroes. To Mary Mackbride, 1 negroe, and at her death to her son Edward Mackbride. To daughter Mary Punch, 1 negro, 1 colt, 3 pounds, & items. To grandson, John Curd, 1 negro. To granddaughter, Jane Mackbride, 100 acres in Goochland. To daughter Mary Richardson, 1 shilling. To daughter Elizabeth Williams, 1 shilling. Not dated Wit: James Young, John Gunn, Joseph Satchawell Recorded December 1742

The wording "only son" was an unfortunate choice because I first took it to mean the testator's only male child with second wife, Elizabeth.  Apparently, though, Edward was his first son with his first wife, and the meaning of the sentence would have been better conveyed using the word "except," rather than the word "only." 

He doesn't call Mary MACKBRIDE his daughter, and he already has a daughter, Mary — the one who married John RICHARDSON.  Is Mary MACKBRIDE really his daughter?  It occured to me that Mary MACKBRIDE might be a daughter of Elizabeth BLANCH, but Elizabeth had a daughter, Mary PUNCH, by a former marriage, so that would just shift the problem of two Mary's from Edward to Elizabeth.  But Edward did named Jane MACKBRIDE his granddaughter, which means one of his daughters had to have married a Mac/Mc BRIDE.  I know of a similar case where there appear to be two Mary's in one set of siblings (viz., the children of Col. Henry CLARK):  one daughter was named Mary and the other Mary Ann, the latter normally referred to as Ann within the family.  So it is possible that "Mary MACKBRIDE" is Edward CURD's daughter; I just wish Edward had called her his daughter in his will (as Col. Henry CLARK did in his will, leaving no doubt in that case). 

2.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).

3.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).