They would definitely be of Wellbelove lineage, because his MOTHER was one, and her father was, as well. What you don't know is his paternity - which, quite frankly, means very little in the scheme of things (all he did was provide the sperm, and some dna), unless you hang on dna as the answer to puzzles.
It is also possible that Eliza had more than one child without naming a father, depending on how many of those listed on the GRO are actually hers.