Why can't I translate this as "we are drinking her milk"? Is "seine" specifically masculine in this sense?
But isn't 'ihn' or 'ihr' (I can't remember, clearly) also 'his'? How do we know which to use?
But isn't 'ihn' or 'ihr' (I can't remember, clearly) also 'his'?
No. "his" is sein- (sein Hund, seine Katze, sein Pferd).
Perhaps you're thinking of ihn and ihm, which translate to "him"?
In English, "her" is ambiguous between possessive ("her milk" like "his milk") and objective ("I see her" like "I see him"; "I give her some milk" like "I give him some milk").
German makes a distinction here -- so if you get confused about how to translate "her", think about whether you could replace it with "his" or with "him".
I'm going around in circles. I cannot hear anything, but I cannot move on either.
For "milkshake," it becomes "seinen Milchshake" (because hey, maybe Wir trinken seinen Milchshake).
This and the banana exercise make me think deeper things about you Duo...
what the problem sometimes seine used for her and sometimes used for him everyybody any solution for that
Seine means "his" and the ending -e means it is referring to something feminine or plural. To say her you would use ihre (fem./plural) or ihr (masc./neut.)