No, he was not very famous during his lifetime. He was a well respected as a composer and performer, who happened to be into a rather antiquated style, of which he had an impressive technical command. But he was an employee/servant, because musicians were not seen as we see them today. He was very good at his craft, but the idea of "artist" didn't apply to musicians.

How come he is now a music god? I think it has to do with the taste in vogue during the 19th century among the German romantics, the birth of musicology and the formation of the Western canon.

His music was not frequently played after his death. It was, however, preserved and studied by people who liked his dense style (Mozart, Beethoven, and others were aware of his works and highly respected him and other "earlier masters." His music and his name came back from the grave after Mendelssohn championed it in big events, in which fancy people wanted to revive the great old (German) music. All that study and revival was part of the birth of a new field of study, musicology. That system shaped a lot of aspects about how music is taught.

Speaking of Bach and his sons, I happened to find this album recently (Spotify link). Highly recommended. Here's a Youtube video with an extract.