Amelia might be able to get along with Dylan Davies. He can be shy when meeting new people, but when he knows someone enough, he's really outgoing. Dylan is a vocalist and once had a band during his first - going onto second year before a fight caused them to disperse. He and Amelia are in the same year, so maybe she already knows about the band and the break up and such. They could already be friends?
For Fiona, have Damitrius d'Eath and Kaiden Poliakoff. Damitrius would already know Fiona as they are both sixth years and Gryffindors. I'm not sure if they would be friends or not, considering Damitrius turned to the Dark Followers and abandoned Potter's Army. As for Kaiden, he's a sixth year too, but he's a Slytherin. Kai doesn't exactly have anything against Gryffindors, and he'd personally find Fiona very attractive. So he could be after her, or something?
For either Susan or Neville, I have Hermione. Don't really need to explain much about her, do I? Her personality hasn't changed much since Hogwarts. Then, there's Alexis and Jake too, but they're quite a few years younger than either of them. Jake is twenty and an Order member as well as a Beast Specialist and Alexis is nineteen, a werewolf, a Death Eater and owns the Cafe Twin Montez.