Here are some examples that might help with "sight":
You see a person in a ridiculous outfit and you say, "Oh, what a sight!"
If you meet a person that you haven �t seen for years, you might say, "You are a sight for sore eyes."
Some people faint at the sight of blood.
Now, for your specific example. I wouldn �t use "sight" and "see" so close together in a sentence. I might say, "It is common to see young people hanging out at the mall". (We usually say just "mall" instead of "shopping mall", although "shopping mall" is definitely correct and not totally uncommon). To use "sight", I might say "Young people hanging out at the mall is a common sight".
We also have an expression "a sight to see" (which contradicts what I just said).
Bruce dressed as a woman is definitely a sight to see!
For your second question, "false" is the opposite of "true".
Artificial means man-made - He has an artificial heart.
Counterfeit is usually a physical thing - I found some counterfeit money.
Fake is also usually a physical thing - She is wearing fake eyelashes, and maybe a few other fake parts.
I hope I have helped you.
Bruce