My question is: What is the meaning of Al-Hadi (The Guide) and Al-Mawrith (The Inheritor) among the names of Allah Almighty?

The name of God, "Al-Hadi" (The Guide), is mentioned in Sunan al-Tirmidhi. Its meaning is the One who enlightens His servants and shows them the path to knowing Him, and guides every creature to what it needs for its survival, as in His Almighty saying: "Our Lord is He who gave each thing its distinct form and then guided it" and "Who decreed and then guided." As for "Al-Mawarith" (The Inheritor/Heir), it is not mentioned among the Most Beautiful Names. Perhaps the questioner meant "Al-Warith" (The Inheritor), and its meaning is the One who inherits creation and remains after their demise, as in His Almighty saying: "Indeed, We are the ones who will inherit the earth and whoever is on it, and to Us they will be returned" and "Everything will perish except His Face."