... ohne, daß es sich vom Knochen löst, noch fest ist ? . . .

... oder doch so, daß es lange haltbar ist / sich lange hält ?

brine = die Salzlauge / Sülze . . .

"al dente" usually refers to pasta or rice, or possibly vegetables, but I guess it could be used for chicken, too.

Re #3: My question here is: Is 'haltbar kochen' a term used in Austria (by any chance) ? . . .

... and what does it mean there ? - (See alternatives in #1) . . .

I'm no Hauben-Chef, Daddy (I can boil some eggs and make a salad, though), but I would think it means the chicken doesn't fall off the bone. ;-)

It means

... ohne, daß es sich vom Knochen löst, noch fest ist ? . . .

I've never heard "al dente" in another context than pasta...?! Does it really work here?

... another try: 'boil them for 20-25 min, without them losing their consistency ...' ? . . .

@ #5: Try to improve your skills: Tackle scrambled eggs ! . . .

... and let your pillion rider lend you a helping hand on them! . . . ;-))