En "courage", Sp "coraje" Old French "corage"
 

Clearly English "courage" and Spanish "coraje" are both descendants from the same Old French word "corage".

But judging from the DRAE definition
coraje (Del fr. ant. corages).
1. m. Impetuosa decisión y esfuerzo del ánimo, valor.
2. m. Irritación, ira.

and conversations with native Spanish speakers from Mexico, the two words have deviated in meaning. The Spanish noun "coraje" means primarily "impetuous" and "irritating". In the Wizard of Oz,el León Cobarde always wanted "valor".

But most online dictionaries would translate "coraje" first as "courage".

I have two questions.
(1) Is their a linguistic terms for two words that have the same ancestor, but now have different meanings?
(2) Is the interpretation that the English and Spanish word have different meaning hold in Spanish from other countries besides Mexico?

'False friends' is the term you're looking for. False friends have the same ancestor but have divergent meanings.
'False cognates' is the term for words that look like they have the same ancestor but do not.

The second meaning of 'irritación' is understood in other Central American countries. My dictionaries list it as being used in Mexico and Spain. So, we need to hear from some of the South Americans to determine how universal it is.
Note that both meanings are used in Cental America and Spain. English has a whole bunch of words with more than one meaning. So does Spanish. Context makes the usage clear.

I've heard Mexicans in the U.S. use coraje for strong anger (beyond irritation.) The adjective bravo also, I've gathered, is more likely to mean fierce and ill-tempered than valiant, unlike the English brave.

One of the definitions of "coraje" in the DRAE is "valor". My friend from Mexico says that is true on paper, but in reality it is considered a quaint, and old fashioned definition.

It would be like using the English words "betide, begotten, benighted, bestride, becalmed, and beheld". Most people know their definitions, but the words have fallen out of normal usage.

As an example, he gave the following lines from an Argentine comedy group. It is difficult for me to understand why the lines are funny, but then I would have trouble explaining why Monty Python lines are funny to someone who doesn't speak English.

¡Firme! ¡Firme ante el enemigo!
¡Con coraje, Don Rodrigo!
Y Don Rodrigo firmó la rendición.

The joke is a double entendre.

What was meant:
firme ante el enemigo = steady against the enemy
¡Con coraje! = courageously

What was understood:
firme ante el enemigo = sign before the enemy
¡Con coraje! = defiantly, angrily

firmó la rendición = signed a surrender

They are called Les Luthiers. :)