Which one is the complete subject:

'The showy gilrs'
'The showy girls in the red sports car'

Our vacation to Niagara Falls was awesome.
declarative

A complete subject is the simple subject and all the words that modify it. Without seeing the whole sentence, it's hard to say.

Declarative is correct.

Also, there's no need to change names.

The showy girls in the red sports car were stopped by a police officer when they ran the red light.

I believe it is the 2nd one.

Yes, you're right.

The complete subject is the noun or noun phrase that tells us what or who the sentence is about. In the given choices, "The showy girls in the red sports car" is the complete subject because it provides a more specific and detailed description compared to just "The showy girls."