Lol I thought it was Lannister at first too XD I actually think the Lannisters are more like Slytherins despite how the colors and the animal are the same as Gryffindor, but just in this case the "Slytherins" aren't all complete jerks .... well not REALLY :3
I love all the posters, but I have one minor critique with the Gryffindor one. Now while there are many loyal Gryffindors out there, I don't think it's a trait that really signifies who they are. It's definitely a trait that you see in Hufflepuffs, which you also had on their poster. Of course it's your poster for the houses, and you can do what you like (obviously since you did it), but just one small critique (is it even a critique? I don't know).