can you recommend a reference book. I bought 2 birds not knowing they were male and female and now I have greys and whites.

Birds on Safari offers DNA testing. From what I understand that is the most accurate way for finding out whether you have male or females. And I believe it's only like $35

Best way to sex a bird. Its noninvasive and doesn't stress the bird.

Some species are dimorphic but if the birds you bought are not then DNA testing is the best way. What species of birds do you have?