Here’s a concise, natural-tone analysis of the phrase "shinseki no ko to otomari dakara aki" (親戚の子とお泊まりだから秋).
Note: I treat this as a short Japanese sentence/phrase; I assume you want interpretation, nuance, and possible contexts. If you meant something else (song title, poem line, or different punctuation), tell me and I’ll adapt. shinseki no ko to otomari dakara aki