Answer:
If Luz is a child, it would be tú.
If Luz is an adult, it would be ustedes.
Explanation:
This is what I know from my Spanish class hope this helps!
first is tú,second is usted, I'm not sure:/
Probably your living room
Yes it can be used in a sentence correctly but it is not very normal or used, much.
Answer:density
Im not pretty sure of the last answer I wrote but I hope this helps!