What is the relationship between Antigone and Ismene?

To answer simply, Antigone and Ismene are sisters. They are the sisters of Polynices and Eteocles, who die prior to the start of Antigone. They are the daughters of Oedipus, and Creon is their distant uncle. (I've attached a family tree in the link below.) 

At the start of the play, Antigone and Ismene squabble over Antigone's choice to bury Polyneices, who has been ordered by Creon to have a sky burial. (A sky burial...

To answer simply, Antigone and Ismene are sisters. They are the sisters of Polynices and Eteocles, who die prior to the start of Antigone. They are the daughters of Oedipus, and Creon is their distant uncle. (I've attached a family tree in the link below.) 

At the start of the play, Antigone and Ismene squabble over Antigone's choice to bury Polyneices, who has been ordered by Creon to have a sky burial. (A sky burial is when a body rots out in the open and is left to be consumed by animals, etc.) Antigone believes that Polyneices deserves a ritual burial, but Ismene is worried about disobeying Creon. These points of view speak volumes about Antigone and Ismene's characters. Antigone is rough and a leader, whereas Ismene prefers to follow and obey. However, despite their character differences, the sisters seem to have had a healthy and sisterly relationship in the past.