Antigone denies that in another way. Being alive means staying with Creon, but belonging to death means staying with dead brothers who know whose act it was.

Ismene said that "they are equally guilty", whereas Antigone denies it without any doubt. From Ismene perspective, Ismene is guilty, because Ismene betrayed her family, and Antigone is guilty, because she break the laws made by Creon. Ismene still consider Creon as justice. However, Antigone is totally not guilty from her own perspective.It is because burying her brother is with justice.

"envy" has strong emotions inside. It is not a word which can be replaced by "admire". By saying "envy", Antigone expressed her thoughts that I still wanna be alive, even if she added "shall not". "envy" can represent "very want something", and emotions inside imply what level it is. However, what Ismene has done is against the family. That's why Antigone shall not do that.

By saying "save yourself", Antigone still cares about Ismene. "saving yourself" is equal to "taking care yourself well". If bonds between families still exist, the care between sisters can still maintain.

Why dose Ismene ask for Antigone's permission, If she is willing to do so, Ismene can confess without anybody's approval.