what prepositions should be used with superlative degree?
can i say
i am the tallest of all the family members?
since sometimes "in" is used in such places as in " the tallest structure in the world" or " the best student in the class"
One preposition belongs to the superlative comparison; the other doesn't.
"of" belongs to the comparison.
That is the tallest structure of any structure in the world.
That is the tallest of any structure in the world.
He is the best of the students in the class.
I am the tallest of the members in my family.
Since the second preposition doesn't belong to the comparison, it can be anything:
That is the biggest mountain (of all mountains) under the sun.
That is the biggest battleship on the seven seas.
She is the prettiest girl among the group.
This is the tallest building outside the United States.