Which one is correct?
They is plural so the object should be plural too right?
They have a good nose
They have good noses
Michael Jackson is white as snow
Is this correct? Is it okay to descibe someone who is not a white person but white like snow white?
They have good noses -- Yes, unless there is possible confusion, a consistent plural is sylistically better.
Michael Jackson is (as) white as snow-- Yes, you can use this to describe MJ's vitiligo.