They could have a son named Albus, after Albus Dumbledore. He might be a brilliant wizard with a strong sense of justice, just like his parents.
Voldemort's remaining followers could be antagonists. They might see the baby as a new threat or a potential weapon. They could try to kidnap the baby to use its power for their own dark purposes.
In fanfiction, werewolf Harry Potter and Hermione could have a very strong bond. Harry's werewolf side might make him more in touch with his primal instincts, and Hermione's rationality could balance that. They could form a connection based on mutual understanding and the need to protect each other from the threats that come with Harry's condition. For example, Hermione could use her magic to create safeguards during the full moon.
Perhaps a family of magical scholars. They would expose Harry to all kinds of ancient magic texts and theories. This would make Harry not only a better wizard in terms of practical magic but also in understanding the deeper roots of magic. They could be the ones to finally unlock the full potential of Harry's magic, which was stunted by his difficult upbringing at the Dursleys.
It could be an old pure - blood family that has been in the background in the original series. Maybe the Blacks who have some complex family dynamics already and taking in Harry could add a whole new layer of drama.
Voldemort could still be an antagonist even if they are trying to change the future. His dark magic and his followers might oppose Harry and Hermione's attempts to rewrite history in a way that doesn't benefit them.
Hermione would be a likely companion. She loves learning and exploring, so she'd be eager to go on a traveling adventure with Harry. Ron might also tag along, especially if there's a chance of food and adventure. Neville could be another option. He has grown a lot in courage and his knowledge of plants could come in handy in different magical environments. Luna Lovegood would be a very interesting companion too. Her unique perspective on magic and the world would add a lot of fun and mystery to the journey.
Another possibility is that the heiress could be a new character entirely, created by the fanfiction author. She could be from a foreign wizarding family that has a claim to something in the British wizarding world. This new character could bring in different cultural elements of magic and challenge the traditional ways of the Hogwarts - centered wizarding society.
Obviously, Harry Potter himself would be the central character. Then, Hermione Granger could be one of the members of the harem. She is intelligent and has a long - standing friendship with Harry. Ginny Weasley is also a likely candidate as she has a romantic interest in Harry in the original series. Luna Lovegood might be another, with her unique and dreamy personality adding an interesting dynamic to the harem.
Hermione would definitely be one of his allies. She is smart and would be able to help him research about his new identity and how to control his powers. For example, she could find ancient texts in the Hogwarts library that relate to both the wizarding world and the Greek gods.
His friends from Hogwarts could still be his allies. Hermione would use her intelligence to help him understand his new situation. Ron would be there for moral support. Additionally, any friends or allies that Rias has in her world could also become Harry's allies. They might be magical creatures or other powerful mages.