人性 is a title that is the essence of what it means to act and be human.

These two characters refer to the way we are as people.

人性 is also sometimes translated as human personality, human instinct, humanity, or humanism.

The first character literally means human or people.

The second character means nature. It can also mean property, quality, attribute, or essence. It can even be a modifier like “-ity” or “-ness,” which is why this word is also translated as “humanity.”

人類 is the way to say mankind or humankind in Chinese.

It's kind of the “animal title” for humans. 人類 is the word you would use if you said this phrase in Chinese, “Mammals include dolphins, monkeys, dogs, and humans among others.”

人類 is a weird selection for a calligraphy wall scroll. But a customer begged me to add this word.

人道 is literally the “The Way of Being Human,” or “The Human Way.” It can also be translated as “humanity.”

人道 has a secondary meaning of “sidewalk” as in “the way for people to walk” (in Japanese and Korean only). But as calligraphy artwork, nobody will read it with that translation.

Please note that there are two ways to Romanize Dao or Tao (Daoism = Taoism). It's the same word in Chinese.