But I don't think they are the people I am looking for....
In answer to questions(posted elsewhere), John did indeed marry Martha Wilkins in April 1860. Marriage certificate lists both parties as being "of full age", and father Jacob, "formerly a Coachman".
Assuming he was the son of the earliest marriage, to Margaret Pitman, he would have been born around 1848/9, making him only 12 at time of marriage to Martha. I'm guessing that "full age" meant at least 21, so this would not be possible - he would have to have been born 10 years before this.
Is there another Jacob Tackley known of at this time? Lack of definite ages means that I have so far reachd a dead-end!