Ist time lucky

Nest inspection
first pair to nest were totally tolerant

sat happily in secluded compartment through their bob-hole
while I inspected

but very light sitters
a 3-day youngster accidently dragged & dropped from the nest
warmed by blowing on in cupped hands and
popped back into nest
parents totally unfazed

Parent-rearing
well, this pair did - for this round
4 eggs - 1 dead in shell, smallest died at 14 days
(think I fed too few Pinkies at the start)

2 fledged - beautiful (cock youngster on the right)
parents back on five eggs still with independent youngsters (hmmm)

from the above you could think parent-rearing is the answer.  This pair certainly fooled me.

this same pair went on to lay various clutches - some in the nest, some on the floor
sometimes they sat for a few days, had a day or two off, then re-sat
became the lightest sitters I have ever known
the eggs were invariably useless by the time I inspected and found a clutch

yet the husbandry was identical to when they had a successful round

a second pair has laid several fertile eggs but not hatched any

third pair laid 5 eggs - failed to sit - by time I found them they were useless

conclusion - these wild caught birds are very unreliable parents (certainly when kept in cages)

for me - fostering is the only way to proceed to get numbers up - then perhaps try parent-rearing with the domestics