To answer your questions above:

1) The piping will only compress the bellows if the forces on each flange of the bellows can overcome the pressure thrust. And then you have those same forces acting on the restraint and pump.

2) If you have an expansion joint with directional anchors on either side of it, then I believe it will act like a tied-bellows. The pipe is "free" to laterally displace, but the piping is locked-in axially.

Have you looked at pressure-balanced bellows? They make an inline type, and a type that basically has a bellows at the nearest elbow. Perhaps they can help.

I hope this helps. Bellows design is confusing and talking with a manufacturer's engineering team will help.