If you had them for 2 yrs and and the other fellow had them before you and the owner before him said they where "proven" , If their only 10 yrs old ,I think somebody lied along the way. Most of my breeders don't produce viable eggs until they're about 10 yrs old and have been "practicing" for a season or two. Rarely is the first clutch viable in my experience. If this is their first viable clutch then issues with raising/ feeding babies is a very real possibility. Good you have the brooder ready to go. I keep my nest boxes on the outside of the cage for many reasons. I also have a door in the back that allows me entrance. I use a piece of thin sheet metal that slides between the box and the cage that allows me to close the entrance hole to the box. This allows me to inspect the eggs/chicks when the hen does leave the box for a few minutes. The small video cameras also work well but you need the ones that work in low light. Back to the eggs. I would let them set the eggs for maybe a week longer than the 28 days after the last laid. So long as the hen doesn't start incubation, the eggs could still be viable for several weeks after being laid. You can only assume when the hen started incubating. My first choice would be to candle the eggs and pull them if not viable, this is your best chance at a second clutch and have babies this season. At this stage of incubation it should be very oblivious if they are good. BTW welcome to the forum. Breeding is not always a popular subject on this a companion parrot forum, i'd like to be able to keep this on the open forum so others can learn about their birds. You can always PM me if you need to. Good luck and let us know if you have questions.