The son could be highly adaptable. Growing up with two such different fathers, he would be exposed to different ways of thinking. He might have Draco's slyness when it comes to getting out of tricky situations, but also Harry's selfless nature when it comes to helping others. He could also be very good at magic as he would inherit the strong magical genes from both his fathers. And he would probably be a bit of an outcast at Hogwarts, not fully fitting into either the Slytherin or Gryffindor mold.
One trait Harry might inherit is a strong sense of self - preservation. Poison Ivy is always looking out for herself in her own world, and Harry could have that same instinct. This could make him more cautious in dangerous situations. Also, he might inherit her ability to blend in with her surroundings. Since Poison Ivy can use plants to camouflage herself, Harry could have a natural knack for hiding or remaining undetected in the wizarding world. Maybe he could use magic in combination with this ability to stay out of harm's way more effectively.
If Harry is Salazar, he might have enhanced Parseltongue abilities. Salazar was known for his connection with snakes, so Harry could communicate with a wider variety of serpents and perhaps even gain more control over them. For Draco as Godric, he could have a stronger affinity for Gryffindor - like magic, such as a more powerful Patronus, perhaps in the form of a lion, representing Godric's courage.
She could be really kind. In contrast to Draco's sometimes haughty attitude, she might be the one who is always helping out the first - years, showing them around Hogwarts and making them feel welcome.
One adventure could be related to a mysterious magical artifact hidden somewhere in Hogwarts. They hear rumors about it and decide to search for it together. Along the way, they face challenges like magical traps set by previous Hogwarts students or even some dark magic that guards the artifact. But because they are twins, they have an unspoken understanding and are able to use their combined skills - Harry's bravery and Draco's cunning - to overcome these obstacles.
He could be very intelligent like Hermione. He might have a sharp mind for magic and academics. Also, he could inherit Draco's sense of pride and self - assurance. Maybe he's a bit of a loner at first because he feels different from the people of the past, but as he gets more involved in the story, he becomes more sociable.
In the fanfiction, Draco's shop could have a special love potion. However, it's not the regular love potion but a more refined version that has a milder effect. Also, there could be a potion that helps with sleep, which is much needed for those who have trouble sleeping due to nightmares caused by dark magic.
He could use a truth - revealing spell like Veritaserum. This would force Draco to tell the truth, and Harry could judge him based on his honest answers. But using such a spell is unethical without proper authorization, which could also cause problems for Harry.
Draco's character development might involve him breaking away from the traditional Slytherin values. Being Harry's brother, he could be influenced by Harry's Gryffindor - like qualities. He might start to question the pure - blood supremacy ideas he was brought up with and become a more inclusive wizard. For example, he could start making friends with muggle - borns, which is a huge shift from his original character.
Well, she would likely be highly intelligent, taking after Tony. She could use her smarts to solve problems in a creative way, much like how Tony built his suits. From the fem Harry Potter side, she might have a deep well of empathy. This would make her care about others and be more inclined to help those in need. And she'd probably be a bit of a maverick, not afraid to break the rules when she thinks they are unjust, just like her two 'parent' characters from different fictional realms.
Well, Si could have a strong sense of loyalty. As Ruby's twin, he would be deeply connected to her and by extension, her friends. He might be a bit of a strategist, always thinking a few steps ahead. He could also be more in touch with his emotions than Ruby, who sometimes seems to be all about action. This could make him the one who provides emotional support to the group when things get tough. And perhaps he has a creative side, coming up with unique solutions to problems that the others might not think of.