Maybe there are some rogue werewolves who don't like the idea of Jake having a half - vampire baby. They could view it as an abomination and try to harm the baby. Another possibility is a new group of vampires or werewolves that emerge, with different ideals and see Jake and Bella's family as a target to gain control over the area or resources. They could be more ruthless and not care about the family's well - being at all.
There could also be a human antagonist. Perhaps a group of hunters who discover the existence of the supernatural baby. They might be afraid of the unknown powers the baby could have and decide to eliminate the threat before it grows up. Or it could be an individual with a vendetta against either Jake or Bella, and now they see the baby as a way to get revenge on them.
It could be some of the traditional antagonists from the original story, like the Volturi. They might see the baby as a threat to their power or the order they've established in the vampire world.
In this fanfiction, there might be some werewolves who view the baby as an abomination since it's part vampire. They could try to harm the baby, which would put Bella and Stefan in a difficult position to defend their child.
The Volturi could be antagonists. In the Twilight universe, they are the powerful vampire coven that enforces vampire laws. They might see the baby as a threat to their power or a violation of their rules. They could try to eliminate the baby or control Bella, Edward, and their family.
The Volturi could be antagonists. Since they are the vampire authority, they might see the baby as a threat to the vampire world order. They could be worried about the baby's mixed heritage and its potential power, so they might try to eliminate the baby and even Bella and Klaus. Another possible antagonist could be some of Klaus's old enemies. They might see the baby as a way to get revenge on Klaus, either by kidnapping the baby or causing harm to it and its parents.
Another possibility is that there is a mysterious figure who has some sort of vendetta against the family. This figure could be causing strange and unexplained events to occur around the baby, like making the baby sick in a way that doctors can't figure out at first. This would then be a source of conflict as Bella and Sam try to protect their baby from this unknown threat.
It could be their families if they are against the idea of Bella and Embry having a baby. For example, if Bella's family has high expectations for her and doesn't think Embry is a suitable partner, they could try to interfere and cause problems.
It could be that some of the humans who have discovered the existence of vampires and the new baby become antagonists. They might form a group to hunt down the Cullens and the baby, fearing that the baby could be the start of a new vampire - human hybrid race that could overpower humans.
The plot could also involve the reactions of their friends and family to the new baby. There could be jealousy from some, like other characters who might have had feelings for either Jake or Bella in the past. Or it could be a story of how the entire community comes together to support them. The baby could also be a symbol of hope for a future where the different supernatural species can co - exist more peacefully. Jake and Bella would then be at the center of this new era, guiding their child and others towards a better world.
Well, it could be a group of vampires or werewolves who see the baby as a threat to their existence. They might believe that the baby will grow up to be a powerful force against them, so they try to eliminate the baby.
It could be the Volturi. Since the baby is a vampire - human hybrid, the Volturi, who are very strict about vampire laws, might see the baby as a violation of their rules and try to eliminate it.
One possible antagonist could be an evil scientist who wants to study the baby's unique genetic makeup. Since Shadow and Blaze are both special characters, their baby would likely have an interesting genetic combination that the scientist could use for his own malicious purposes.