Do you capatalize twin towers

Answer 1

It depends on what context it's being used in.

For example: The World Trade Center was centered around two twin towers...

Here you wouldn't need to capitalize them because they're not being used as proper nouns. They're just a type of building that you're describing.

However, if you were to say:

The day the Twin Towers were destroyed will be forever remembered.

You need the capitals because you are referring to two specific buildings and the phrase is being used as a name, thus making it a proper noun.