What Am I Riddles

Question: You see us everyday, but you never see us together. We appear everywhere but never are we together at the same place. Who are we?

Question: I can be seen, I can be not. Thanks to me, you'll fall in love. I mostly am sweet, but once I were sour. You can receive me, you can't just buy me. You only can send me, or simply share me. What Could I be?

Question: What grows when it eats, but dies when it drinks?

Question: What has four legs and can't walk?

Question: A dad and his four boys stand in line.
All crowned, they toil in darkness.
Another family they see, two birds of a feather.
All of them together clad in leather.

What are they?