I take it you didn't buy it 4 years ago and have been loitering in LZ wondering how to compose you're first post?
I take it you have only just bought this vehicle?
If so - give it back to them, ask for your money back. They should not judder on full lock. Do you think LR would have sold any of therm if they did!
They may be right about the tyres, it is a reason why AWD vehicles break. As such they shouldn't have sold it to you like that. Depends how mismatched they are, if they are a different make/model of tyre then that's a catagorical no-no even on a F2 I would have thought.
The vehicle almost certainly has a problem with its tyres and/or Haldex and/or rear differential.
Previous owner has recognised this and got rid cos he/she found out how expensive it is to fix that sort of stuff. You should get your money back you do not know what sort of damage has already been done.