R' Jacob Landau

From Chapter 7, page 155 of "The Unbroken Chain" (3rd edition), by Neil Rosenstein:

G12.1 R. Jacob Landau, married the daughter of R. Joshua Friedensohn....

Regarding G12.1's father Isaac, a footnote at the bottom of the page states the following:

R. Joseph Lowenstein in an unpublished manuscript (a copy in posession of the present author) states he was married twice and had issue with his second wife, connecting their son Jacob to the Friedensohn family.
(Rabbi Lowenstein's source, however, is published: Rabbi Y.M. Biederman's genealogical tract on the Halberstadt family, printed in several works; his father-in-law was Jacob's brother.)