Worst Father/Parent in FF

[Sephiroth]

Brahne to the point where she actually is responsible for this - it ends at the point where she just cannot do anything against Kuja's spell.

Overall as mother without that she was a very good mother for Garnet her whole life.

Hojo until the point where he wants to strengthen Sephiroth. Educational he was nothing just some guy who made Sephiroth the super soldier he is. Same goes for Hollander.
Cidolfus for being an absolute douchebag.
Jecht is not a bad person but he just should not have made Tidus feel that way. Tidus was a kid that wanted attention from his parents and was mad when his mother died, et cetera. Jecht is not really a bad father on the same level the villains are.
Same goes for Bartholomew, Hope's father.

So Hojo, Hollander and Cid.

Also good job King Cornelia for letting your daughter be kidnapped by some random knight.

Definitely Hojo. He experimented on his kid, even in the womb -- resulting in his mother's death.

Sephiroth was the result of JENOVA cells in the womb before fertilization. That is why Lucrecia has JENOVA cells inside her. She was injected with them, not really Sephiroth. This is a mistake of two different dialogues that is supported with Crisis Core - though there only Genesis and Angeal are explained. But Vincent in Dirge of Cerberus says: "An experiment on your own child?"

Still - Lucrecia has the JENOVA cells so she must have been the one being injected with them and they fused with the zygote during fertilization (or a bit afterwards, that is really not so important, the thing is Sephiroth is unique and has JENOVA cells actually as parental cells and not only Lucrecia and Hojo's).