Seems clear to me, VG first post.
Other runners' positions are not determined by the timing of the OBS.
If the ball becomes dead because of an apparent putout of an obstructed, then check the others. There is a rule of thumb that progress 1/2 way is awarded forwarded, but in your case, the runner is "
most of the way there at the time F2 tags R1"; so 3rd base.