There is no chance the hub bushes have survived 126k and the trailing arms will be knackered at that mileage.
Hub and transverse arm bushes will fail the MOT when they are physically broken, but the car will handle badly long before an MOT fail. I've never seen a trailing arms actually break, but they do go soft.
You don't say how long you've had the car, but there is a lot to be said for replacing all the rubber bits on a car you've just acquired.
- trailing arms, very easy, just unbolt
- hub bushes are a pain to get out and I would replace with poly. Not because poly handles better, but because it is easier to change next time.
- transverse arms are easy as long as the big bolt in the hub comes out without a fight
Do the front as well and then get it 4 wheel aligned. A 156 with good suspension should feel like the rear wheels are directly behind the driver's seat. If you feel the back swinging around, then it is knackered.