Re: Sims behaviour that's odd.
@hoxharding It sounds to me like it's working just fine, you just don't understand what's going on.
When things get that green/dirt stuff on them, they're just dirty. They get dirty through normal use and you just need to clean them. (Click on it and select 'clean') You can also upgrade a lot of things to "auto-clean" if you have handiness skill, or you can also hire a maid to clean for you.
Sometimes using a shower will get water on the ground, or when a sink or toilet breaks, water will get on the ground. You just need to mop it up.
If the sister was flirting with her brother, were they blood siblings or by marriage? Blood siblings can't flirt. Siblings by marriage can (I think).
I think siblings can become broken and flirt, but that's rare. It's never happened to me. There ARE mods that disable family romance restrictions, but you said you don't use mods.
Magic Sims will never use spells on their own. They may "practice" magic, but not cast spells. If a sim used the freeze spell (Chillio), you must have clicked it accidentally. There's also the "Sim Ray" you can get through a few ways, but normally from the Scientist career. It can "Freeze Ray" a sim. I think you can also buy the SimRay from the computer's gift menu.
Just keep playing, it's still a lot of fun. I doubt anything's broken.