Heading out, but adding a quick note for now that I think the Sarah of the article was a daughter of Isaac by his first marriage. The will was being disputed by her and other siblings of the first marriage, who alleged their step mum mistreated them and forced their father to alter his will. Some of Isaacs brothers are also brought forward in support of their claims.
Certainly, the article seems to be about the same Isaac who as a widower, married Eliza Jane Ferris. Not seeing either of the disputed wills on PRONI though, but maybe someone else can double check.