Yevamos 4:5-6

Yevamos 4:5

The responsibility to perform yibum falls to the oldest surviving brother. If he is unwilling, they go to the other brothers. If they also decline, they return to the oldest brother and instruct him either to undergo chalitzah or to perform yibum.

Yevamos 4:6

If the eldest brother wants to wait until a younger brother reaches the age of majority, or if the next-eldest wants to wait for the eldest to return from overseas, or if they want to wait for a brother who is deaf or mentally incompetent to recuperate, they do not listen to him. Rather, they insist that he either undergo chalitzah or perform yibum.