Yes, she was, although this promise was unknown to her or her mother Demeter.
Because Zeus promised Persephone to Hades as his wife.
Because Zeus promised Persephone to Hades to be his wife. Zeus just neglected to inform Persephone and Demeter of this.
Zeus is Persephone's father. He promised her to Hades to be his wife. However, he neglected to inform Persephone or Demeter of this promise.
Hades was promised Persephone as his bride by her father Zeus. But Zeus did not inform Persephone or Demeter of this. So when Hades went to claim his bride it turned into an abduction.
Zeus promised his daughter Persephone to Hades, so Hades could take her as his wife. However Zeus neglected to inform Demeter; Persephone's mother, or Persephone herself of this. So when Hades appeared to claim his bride, it was an act of kidnapping, instead of simply retrieving her.
Because she was promised to Hades by Zeus (her father) to become Hades' wife.
Hades took Persephone to the Underworld to be His wife. Zeus (Persephone's father) promised Persephone to Hades as his wife.
Hades was promised by Zeus that he could take Persephone as his wife. But Zeus neglected to inform Persephone or Demeter (Persephone's mother) of this. So, Hades sprang up from the earth and abducted Persephone, to take her with him back to the Underworld.
Hades is Persephone's uncle. Because Zeus is Persephone's father, and Hades is Zeus' brother.
The first time she saw Hades she was afraid of him and very upset, since he abducted her. Zeus promised Hades that Persephone would be his wife, but neglected to tell either Persephone or Demeter of this.
If you are asking 'did Zeus allow Hades to marry Persephone', then yes, he did.
hades father in law is Zeus because persephone is his wife and her father is Zeus makeing him hade father in law along with being his brother