Typically, when the rear suspension carrier fails, the car sags and there is a clunking sound when the transmission goes from neutral to reverse or drive.
You mentioned a rear axle vibration. There are many causes:
U joints, differential failure, driveline carrier bushing, wheel bearings, tire/wheel balance, axle shafts, etc.
A concern is how difficult it is to remove this suspension carrier.
What condition is the rest of the rear axle suspension bushings?
Such as rear axle locating strut, rear axle suspension carrier pivot, axle shafts,
Sub frame mounting, etc.
Need to proceed slowly and inspect the rear axle, driveline and suspension carefully.