One way is to educate people about the importance of not believing and spreading unsubstantiated rumors. Encourage critical thinking so that when people hear such a story, they question its authenticity.
If it's just a story and a misunderstanding, the first step is to clarify the situation. Talk to your sister and uncle separately to understand what really happened. Maybe there was a misinterpretation of an innocent action.
This is a very uncomfortable situation indeed. You should start by taking responsibility for your actions. Let your little sister know that what she saw was not appropriate for her to see. If she has questions, answer them as simply and appropriately as possible. For example, you could say it's a normal but private activity for adults. After that, work on your self - control and privacy habits to avoid similar incidents in the future. It's important to also respect the fact that this might have an impact on your sister's view of you, so be extra careful in your interactions with her going forward.
If'mom caught sucking stories' is a rather strange or unclear statement, it might be a misphrasing. It could potentially refer to mom being caught up in stories in a way that seems excessive. For example, if she's always on her device reading stories instead of doing other important things like household chores or taking care of kids, and then got noticed or 'caught' doing that.
It depends on the context. If it means she was caught enjoying stories, it could be a good thing as it shows her love for literature or knowledge. It can be a form of relaxation for her.
Sharing such stories is highly inappropriate and disrespectful. Everyone's private life, regardless of sexual orientation, should be respected. Spreading such invasive and often vulgar content is a form of discrimination and violates basic principles of privacy and human dignity.
If you caught your sister doing this, it's a sign that she may not understand appropriate behavior. Immediately remove her from the horse in a gentle but firm way. Try to explain to her that horses are living beings and we should not engage in such actions. And it might be a good idea to keep a closer eye on her when she is around animals in the future.
If you catch your little brother jerking off, it's an extremely awkward situation. First, try not to overreact. You could simply leave the area quietly to give him some privacy. Then, later on, you might consider having a general talk about privacy in the house without specifically mentioning the incident. For example, you could say that everyone needs their own private time and space.