"Your grandmother is drinking milk."
Translation:Twoja babcia pije mleko.
I'm a little confused. 'Twoja babcia' means your grandmother belonging to one person, but does 'wasza' mean your grandmother plural, as in talking to multiple family members regarding their grandmother? (Sort of a ty and a wy situation?)
*takie dobre pytanie
The English sentence is a little ambiguous in that matter and for this reason Duolingo should accept both „twoja” and „wasza” in the answer. If you were marked wrong for either, please report it.
Is mleko in accusative? Am i to understand that for inanimate objects the nominative and accusative are the same?
Yes, it's Accusative.
Accusative is identical to Nominative for:
masculine singular inanimate
not masculine-personal plural