i say slytherin because that lily and also albus since I see lily as a ginny but an ext cheeky and sly however James together a griffindor :)
Well, there is no canon top top this, in the books or otherwise, therefore I"ll do a canon-based guess.
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J.K. Rowling has created that families often enter the same residence as their ancestors. Albus Severus was pretty dead collection against going come Slytherin and Harry assured him the the Sorting Hat would certainly take his wishes into consideration. Both Ginny and also Harry to be Gryffindors, together were Harry"s and also Ginny"s parental respectively, also as all of Ginny"s siblings. Ns think Gryffindor provides the many sense.
Edited to add: ns thought about this a small bit more and i can"t help but wonder if any of Harry"s children had an ext of a opportunity of going to Slytherin if it wouldn"t have actually been James. While i won"t go so far regarding suggest James is a bully, he absolutely gives Al a hard time in ~ King"s Cross and deliberately provokes Al"s anxieties.
Further, J.K. Rowling has actually said that, although harry wouldn"t have outright offered the Marauder"s Map to any of his children, James would"ve to be the boy to find the map in Harry"s desk and also nick it. It seems clear from canon that James is a Gryffindor, but he seems to walk a little on the wild side, a trait that Slytherin prizes (for confirmation view "Is Slytherin Evil" below on SFF or Dobby"s Reward in Chamber that Secrets whereby Dumbledore defines to Harry the Salazar Slytherin did compensation "resourcefulness, determination, and also a specific disregard for the rules.") perhaps James had a close speak to with the Sorting Hat, prefer Harry, and also was projecting his own are afraid of Slytherin top top Al by ribbing him. Again, simply an idea, however one v canon in mind.
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We really understand nothing around Lily, other than that she"s two years younger 보다 Al and can"t wait to walk to hogwarts herself. There"s naught in the epilogue to yes, really delve right into what properties Lily has and what house they can qualify her for, therefore I"ll stick v Gryffindor because that Lily because of the family members connections.
ETA: Harry Potter and the Cursed Child (released 07.30.16) clarifies that James and Lily Potter checked out Gryffindor, while your brother Albus Severus went to Slytherin (w00t!).