Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
I would say that your son has overheated and worn the clutch, and now you have "clutch shudder".
Very common to many cars.
Would require transmission removal for repair, would recommend a new flywheel and clutch assembly.
I would also not use an X-Trail for 4WD, not aren't up to the rigors of real 4 wheel driving.
They are a good commuter for the city, people mover etc.
I hope my advice to you has been of some help.