okay with a mate it's a different story..... the males do go in
for quite a while sometimes before the female does and maybe you
didn't leave it long enough. have you put the eggs in the nb?
you say you took the nb out? it should be attached to the
outside of the cage in a high up position so you have access
from the outside. If you don't have a nest box hole in the cage
and don't want to cut into it not sure what to say.
I don't know if oyster shell can get impacted the same as grit
can but I don't trust it so I don't give either. Tiels hull
their seeds and don't need either.
keep giving fresh foods daily forever. one day they will decide
it is truly good foods.
** after thought ** are you sure you have male/female?