"Her endless shadows on your cheeks" is like a metaphor or artistic language. Here it can either be taken literally, or as an abstract idea. It is up to the reader to decide. I would think this means: The son has long eyelashes or defined cheekbones that cast a shadow, and these were inherited from his mother. OR A "shadow" on someone's face can be used to express emotion. This is often a melancholic (sad) emotion. This meaning is more abstract. You could say it means: The son's face shows similar emotions that his mother's face did. Blowing an eyelash is an old folklore/traditional thing people do for luck. When you lose an eyelash, you can hold it in the palm of your hand, blow it away, and make a wish. "There are days when I think someone must have blown all her eyelashes into the ocean just to wish for you." This means the father thinks that someone has made a lot of wishes to help the son. So the son is very lucky in some way.