For Daphne: Susan wouldn't likely get along with Daphne, but that's no surprise. And I'd love it if Stephen and Daphne didn't get along either because he's a) muggleborn and b) is secretly crushing on Tracey and the feelings are mutual. It could be some fun 'drama'. Seamus wouldn't likely get on with her because he has an aversion to anybody that wears green. :P
For Mandy: Susan and Mandy would likely get along, they're both the outdoorsy type so that helps. Susan's easy to get along with for the most part. Stephen of course is a housemate so there will be connections there! He's always been the quiet shy type so it's likely that they're friends, but she doesn't know TOO much about him, because he just doesn't share much about himself. Seamus could go either way, he's fickle like that, but I don't see any reason for him not to like her!
Welcome again to the game and it's good to have you here!