There are three questions throughout the game that determine your ending, with ending A being the result of answering at least 2/3 optimistically, and ending B being at least 2/3 pessimistic answers. I believe the important questions are (from memory):
What does death mean (Infinity A/Oblivion B)
Will Amicus be a good emperor (Yes A/No B)
Should Amicus talk more with Neferu (Yes A/ No B)
The option to refuse the parents' plan just leads to a bad end.