The first consideration with introducing a new character like Andre is figuring out how he's going to integrate into the established social milieu. No it's not! The first consideration is figuring out if Alice will like him or not. From the first indications Alice and Andre may get along Okay.
For most of my characters I've got a vague backstory in mind. For example, Beni has an older sister and a baby sister, Nara has a much older brother, Marcus is an only child, Kevin I'm not sure of yet, Dill has too many brothers. Andre I'm guessing is in the middle of a lot of sisters, maybe six. So, there, that means he can deal with Alice just fine, and it probably explains his noisiness too. But since it's only a vague backstory and I haven't mentioned it, I could change it at whim if it no longer fits in with a gag I've thought up. And I'm not likely to mention all these other characters because I don't want the strip to get too cluttered up with stray people, nor do I want to learn how to draw them.
Which still leaves the problem of Sofie. I'm not sure who she is yet and I'm not real sure I want to find out. Small children for whom so much is novel are always meeting strange new people and sometimes, inexplicably, that strange new person doesn't like them, so maybe that's the limit of Sofie's contribution. And no one noticed that her name was spelled "Sophie" the first time out so I'd better not mention that either.