Some notes.No answer but I've left it so you don't need to go over the same ground
Newer, Oxford Dictionary of National Bio repeats the info from the DNB
"His first wife, whose maiden name was Sambroke and whose given name may have been Sarah (a William Melmoth, son of William and Sarah Melmoth, was baptized at St Andrew's, Holborn, on 17 May 1696), died about this time, reputedly leaving him some property. By 1710 he had married Catherine, daughter of Samuel Rolt of Bedford, and granddaughter, on her mother's side, of Thomas Coxe, physician-in-ordinary to Charles II. They had four daughters—Constantia, Sophia, Catherine, and Jane—and two sons: the author William Melmoth the younger (bap. 1710, d. 1799) and Thomas. Before their marriage Melmoth had to assure himself that an estate to be settled on him as part of his wife's jointure 'was so absolutely his property as to render it a sufficient security' (Melmoth, Memoirs, 44) "
Pasted from <https://www.oxforddnb.com/view/10.1093/ref:odnb/9780198614128.001.0001/odnb-9780198614128-e-18535?rskey=TQmg1A&result=1>
It would be good to be able to find the Melmoth Memoirs reference (original book seems to be Melmoth ' Memoirs of a late eminent advocate , and member of the society of Lincoln's inn '. London , 1796
Profile of Catherine gives a marriage to William Melmoth 21 Mar 1698 All Hallows’ Church, Bread Street, City of London, England. Source - London Church of England Parish Records, All Hallows’ and St John the Evangelist - Parish Registers 1538 - 1831. Unfortunately there is a gap in the registers on ancestry. No register between 1664 and 1723. (edit found a transcript of marriage, see below)
1698 is 12 years before the date mentioned on ODNB
Samuel Rolt MP was son of Thomas Rolt and Mary Cox. History of Parliament
Cambridge Alumni https://venn.lib.cam.ac.uk/cgi-bin/search-2018.pl?sur=Rolt&suro=w&fir=Samuel&firo=c&cit=&cito=c&c=all&z=all&tex=&sye=&eye=&col=all&maxcount=50
Marriage to Susanna Poulter 1692
If Catherine were this Samuels daughter, she would have to have been born fairly soon after his marriage in order to be of an age to marry William Melmoth in about 1710 . No daughter of Samuel and Susannah could have married in 1698.
EDIT Found the 1698 marriage.The entry makes it pretty certain this isn't the correct Samuel https://archive.org/details/registersofallha00allh/page/n263/mode/2up