You have 3 nipples on your calliper? odd, I thought Discos had single circuit callipers unlike the RRC.
Anyhow, the top nipple is one circuit, the other two are the inner and outer of the other circuit. Bleed the top one fiorst, then the inner one, then the outer one.
Don't know if they are the same as LDV, but it wouldn't surprise me in the least.
No idea what the thread is but probably metric, the same as the brake pipe.
If you've sheared the nipple off I'd suggest a new calliper, try Paddock motors
http://www.paddockspares.com/ for cheapness as you risk damaging/weakening the calliper trying to get the old one out.