Brake fluid bleed nipples US.

[DIOGENES]

2000 VW Passat petrol auto.
The local VW agents can no longer change brake fluid as the bleed nipples cannot be moved.
Presumably corroded into the callipers?
They refused to use heat.

Changing the front callipers seems possible at around £90 exchange each.
Rear callipers are more costly.
Once I decide to change callipers it would probably be sensible to also change all pads and disks, so we start getting to big money.
More costly than is sensible for a 16 year old car?

Another garage [ not VW ] also tried but failed to shift these silly little fine thread bleed nipples.
Cars I worked on in 1960s and 1970s all had robust bleed nipples, big enough to cope with forceful removal.

Any ideas on who or what could be tried next?
A broken bleed nipple is no joke, so it is not a job for inexperienced people.
HELP!