TWO RHYMING RIDDLES

1)
We are two sisters without a mother;
Each of us dies in giving birth to the other.

2)
Two brothers are we, each guarding a door,
Both welcomed and dreaded, both joyful and sore;
Our round is eternal, endless our season,
Transcending all men, surpassing all reason.
All flesh before us their places must take,
The wise, the simple, the small, and the great.

Answers:

1. Night and Day
2. Birth and Death