The way you can use these are as follows...
Is there any juice left? Tem suco ainda?
How much do you have left? Quanto mais voce tem?
How much is remaining? Quanto e sobrando?
You can use them together - the remaining six people left in the house were taken to hospital
Os restantes seis pessoas que ficarem na casa fui levado para o hospital.
Faltando - a gente usar missing em vez das outros
I am missing the last piece of the puzzle
Estou faltando a ultima peca da quebra cabeca.
We can say - the dog was missing a leg (voces falam - o cachorro estava sem perna - pode em ingles
Tambem, the dog was without a leg)
Although we would not say, esta faltando muito its missing a lot?
We would say - how long is there to go? How long left to go. Quanto mais demora?
Hope this helps a bit...