Which sentence uses the underlined pronoun correctly?
a.
grandmother cooked all of our a special dinner last night.
b.
grandmother cooked all of we a special dinner last night.
c.
grandmother cooked all of us a special dinner last night.

There's nothing underlined in the question. 

But I can tell you that choices 'A' and 'B' are awkward constructs,
which grate on the ear and sound ridiculous. 

Choice-C, in contrast, sounds as good and tastes as good as
Grandma's special dinner.