I am from the exact line as well as the Askew/Mary line. Still reside in Texas. Britton Gatewood, son of John Washington was my line. Recently uncovered a lot of documents at the General land office on approximate times and Business in Texas. Appears John Washington Askew came to Texas very early - 1818 by his own oath.
I joined the Sons of The Republic of Texas about a decade ago under David Looney. Love my Texas history.
Would LOVE to get a copy of that book you mention.from Norman.