Granted, but so is "docteur." I can address "docteur" directly. Why not "masseur"? Are you suggesting that I have to call him "Monsieur le masseur"? Isn't that a bit precious?
And by the way, why would I not say simply "soeur" rather than "ma soeur." The latter sounds a bit aggressive, n'est-ce-pas?
Docteur is a title (docteur en médecine, docteur en pharmacie, docteur en physique...). A physician's profession is "médecin".
To your "masseur", you will address "Monsieur" or "Jean-Pierre" if you know him well.
Brothers and sisters can be addressed with "mon frère, ma soeur" (same addresses for monks and nuns), or with more affectionate: "cher frère", "frérot", "ma chère soeur " or "soeurette".
Hello girls! = Salut les filles !
There is no ambush or idiom here.
The lesson is about possessive pronouns : le mien, le tien, le sien, le nôtre, le vôtre, le leur // la mienne, la tienne, la sienne, la nôtre, la vôtre, la leur // les miens, les tiens, les siens, les nôtres, les vôtres, les leurs // les miennes, les tiennes, les siennes, les nôtres, les vôtres, les leurs.
All of the latter are translations for: mine, yours, his, hers, ours, theirs.
It is therefore logical that you are shown constructions using possessive pronouns.
"c'est ton chien, ma soeur" back translates to "it's your dog, my sister", both of which using possessive adjectives.
Thanks for your great input. I felt it was idiomatic because the literal English translation that came to mind was "The dog is of you, my sister", which is clearly poor and somewhat nonsensical English. In light of your comments, I now understand why "The dog is yours, my sister" is the logical translation. Mindful also of your comment that "Le chien est le tien, ma soeur", is not in common usage, although otherwise apparently correct, led me to think there was an idiomatic aspect to the "a toi" usage.