Advice please! Help!

Freelander 1 TD4, 2004.
Chaps, could you offer some sage advice? My brother has a beloved TD4. It’s a bit of a shed, full of crap and used for chasing an errant collie. It’s just been sent to a very trusted mechanic as the clutch is slipping a bit. However, when he tried to dismantle the bloody thing, he ran into an issue with a captivated nut. Here is the message:

The o/s/f subframe mounting bolt captivated nut has broken from its weld inside the chassis

Then-

I borrowed a small disc cutter of the farm , cut through only to find another skin and no sign of a nut, so decided to put it back together, when trying to put driver side bottom ball joint in the rear bracket broke , cast alloy, no one has got one so ordered one off the Internet, after all this no further forward, needs someone who does landrover all the Time.

So, that’s where we are. My brother is very very well aware that this will likely cost far more than the car is worth. That’s not an issue, he could drive a new defender if he wanted. He doesn’t!

Could someone offer some advice?

With many thanks.

The subframe doesn't need to be touched to replace the clutch, so that issue shouldn't have arisen anyway.

I've never heard of anyone breaking the rear mount fitting a wishbone.
There are plenty of second hand ones on ebay though.

Captive bolts can break, common with other vehicles and I'm sure your mechanic could either fix by getting to the back of it or google an answer.
If it's spinning then you could grip the bolt (or weld something to hold it with) and cut it off so the captive part falls away, then use a long drill to locate the exact position to cut out the inside of the car.

Many thanks everyone. It’s going to a different garage next week. Hopefully they will be able to sort it out.