A1 in frontcourt passes to A2 also in the frontcourt. The ball bounces in the backcourt, A2 still in the frontcourt, catches the ball after the bounce. Is this a over & back?

It's not an "over and back," but it is a backcourt violation.

Here (once again) are the four qualifications for a BC violation:

(1) Team A must be in control.
(2) The ball must attain frontcourt status.
(3) A# must be the last to touch the ball before it goes into the backcourt.
(4) A# must be the first to touch the ball after it has been in the backcourt.

In your case, A1 was the last to touch before the ball went BC and A2 was the first to touch after it had been in the BC.

Yes, BC violation.

Team control by A at all times
Ball had FC status
Ball went to BC last touched by A
Ball first touched while having BC status by A