How do I know if my budgies are happy???and how do i know what gender they are?

We asked for a male and female but the lady who worked at the store was like 16 and she didnt really look like she knew what she was doing. Im 16 and not a bird expert but from what Ive read they look like two males. I got them 3 weeks ago how do I know if their happy? Theyusually never shut up and they are never still they hop all over the cage and like hanging upside down from their perches is that normal?? Also im feeding them Kaytee Forti Diet Pro- health http://www.petco.com/product/108599/Kaytee-Forti-Diet-Pro-Health-Parakeet-Food.aspx is that a good food?? and they have spray millet.
Heres a picture of them

By the looks of it you have males. When they have blue or purple just above their beek they’re male and when they have brown they’re female. It sounds like they’re happy little birds. If they’re jumping all over their cage and singing all day, they must be happy. And yes that food seems to be really good.
For males, i like the names winston, hamilton, vinnie, addison, birdie, elliot, caden, sammi, preston, bruce, davey & charles

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