This kind of interest is not in line with the norms of a healthy relationship. A good marriage relationship should be built on positive emotions, common goals and positive communication. You can try to introduce some positive literary works or movies to your wife to guide her interests to a more positive direction.
Sharing 'cock cum stories' with your sister is extremely inappropriate. Family is a place of love, care and positive interaction. Such vulgar content has no place in family communication. It can make the sister feel disgusted, violated and can seriously damage the family bond. Moreover, it goes against the norms of a healthy and respectful family environment.
Loving your sister in a proper, family - affectionate way is normal. But the term 'cum' is inappropriate and vulgar in this context. We can talk about heartwarming stories of siblings loving each other. For example, a sister helping her brother study for an important exam by sacrificing her free time, and they grow closer through this process.
I'm not sure which specific 'little sister swallows seed story' you are referring to. There could be many fictional or personal stories with this title. Maybe it's about a little sister who accidentally swallows a seed and then something interesting or educational happens as a result.
The moral could be about being careful. Since the little sister swallowed the seed by accident, it shows that we should be more cautious about what we put in our mouths.
I'm not sure specifically which 'little sister swallows seed' story you are referring to. It could be a very unique or local folktale. Maybe it's about a little sister who accidentally swallows a seed and then some magical or interesting things happen as a result.