If it's cool with Joan and Lily I'm all up for Ted and Remus knowing each other a bit! I can see them getting along except for the part where he stays away from Dora
Remus and Lily FTW! I definitely see them being good friends and getting along wonderfully, except for when she's considering hexing a certain toerag. As for Melanie, that sounds great! Lils needs a sassy girl to hang around! Alexander, you suck. But funny Prefect times sound like awesome!times.
If Melanie and Remus do discover who he is, they best be putting their 'ruh roh' faces on, mkay? And yeah, Antonin might have seen Alexander sitting at the kiddie table at Death Eater shenanigans. =P He also might vaguely remember him when he went to Hogwarts.