Role of the Brother-in-Law
Please note that "Chalitzah" refers to the rite which frees a man and woman from their obligation to perform levirate marriage.
Links
The Brother-in-law
If the Brother-in-Law has intent to marry her, via Chalitzah: Yevamot 106a
Sitting/Standing: Yevamot 103a
The Spit should be in his face: Yevamot 106b