If I use Grand Tree to evolve from Charmander into Charmeleon and then into Charizard ex, can I use Charizard ex's "Infernal Reign" Ability or not?
No, you cannot use Infernal Reign because Charizard ex was not played from your hand to evolve Charmeleon.
Source: TPCi Rules Team (2024-09-26)

Relevant cards

Note: All applicable cards may not be listed below.
SV3_125
SV3_125
SV7_136
SV7_136