Is tien or tienne appropriate is this a formal situation where you would use ‘Vous’?

Hi Katy,

If you use the polite ‘vous’, these will be the wrong pronouns to use . You have to use ‘le/la/les vôtre/s’ just as if ‘vous’ represented several people.

Take a look at the following lesson which will give you more details - 

https://progress.lawlessfrench.com/revision/grammar/how-to-express-ours-yours-theirs-le-notrele-votrele-leur-possessive-pronouns

 

Hope this helps!