bầu dục = kidney or oval?
Yep, bầu dục = oval.
It can be used to mean kidney (though not common at the present) due to the shape, and
bóng bầu dục = rugby
due to the shape, too.
When "bầu dục" works as a noun, it is a kidney, and when "bầu dục" works as an adjective, it is oval/ kidney shaped. We say "rugby" is "bóng bầu dục" since this kind of ball is in oval shape.
according to Wiktionary, bóng bầu dục refers to both American football and rugby. could be some confusion there
Accepts "những" for các here.