In captivity these birds nest in boxes about eight inches square. Don't waste your time and the birds by trying to force them to nest in a finch basket. Parakeets have up to eight babies. Ma and Pa keet, and all the babies, must be able to fit in the nest. If you are not interested in breeding your birds, the sexes don't really matter.
Parakeets are almost always friendly with each other if all placed in the cage at the same time.
Just use common sense and allow the birds some elbow room. Don't over-crowd your birds. If you have had a parakeet by itself for some time, you might be thinking of getting a second bird as a mate or friend for the first. This is a good idea, but don't put the birds together right away. Birds are just the same.