Is your "y" character meant to be essentially the same character as the "j" character but just with an underline beneath it?

Additionally, you say the language is pronounced like spanish. That being the case, how is the "j" character pronounced? (Similar to "h" or similar to "y"?) What differentiates it from "h" or "y"?

Within the context of the imaginary world this language evolved in, if "j" is pronounced similarly to "h" or to "y", have you considered what sort of circumstances may have given rise to two letters in their alphabet having effectively the same pronounciation?