presidency of drupal template file
Answer 1:-template.php file will runs first.you can check it by using die() on top of all files.

answer2 :-For changing some variable's value for page.tpl.php/html.tpl.php use function function XXX_preprocess_page().

html.tpl.php -> Handles meta info, body classes 

page.tpl.php -> Handles content body display

node.tpl.php -> Handles content display

field.tpl.php ->Handles per field display

Template.php provide display alteration  for all these files.