To interpret your dream, it would be helpful to know what was going on in your waking life at the time of the dream, especially as it relates to your family. Given the setting of your dream (your home) and the people in the dream (your sister and father), it's likely to relate to situation involving your family.
To explore the meaning of your dream, here are links to the definitions of the key symbols in your dream...
www.dreamdoctor.com/dream-dictionary/definitions/car.html
www.dreamdoctor.com/dream-dictionary/definitions/driving.html
www.dreamdoctor.com/dream-dictionary/definitions/snow.html
www.dreamdoctor.com/dream-dictionary/definitions/can-t-see.html
www.dreamdoctor.com/dream-dictionary/definitions/house.html
www.dreamdoctor.com/dream-dictionary/definitions/door.html
www.dreamdoctor.com/dream-dictionary/definitions/garden.html
The first part of your dream is pretty straight forward. Your sister was behaving in a way that made you feel as if she was "driving" the action/attention in your life. The good news is that you realized that and took control of the situation. But, it was emotionally "cold" in your life/family at the time, and you "couldn't see" which is dream shorthand for feeling lost or confused.
Without knowing what was happening in or to your family at the time of the dream, it's hard to say who the unidentified man would have been. Because you don't know his identity in the dream, odds are that your dream disguised him on purpose. This often occurs to "protect" the dreamer from an unpleasant awareness. The fact that the "man" has a father with Alzheimers is a clue. It could be a literal clue or a symbolic one, perhaps even an allusion to your own "forgetfulness" about something you'd rather not remember or confront(?)
As for why all of the angst "next door," with a crying wife and kids throwing flowers at your yard... the symbolism paints a picture of a family in distress, one that is uprooting its "garden" and throwing it away.
If you're still confused as to how the dream relates to your waking life at the time you had it, try to remember how you felt IN the dream. Feelings in dreams are never disguised, so how you felt in the dream is how you were feeling about its subject in your waking life. Were you confused, unsettled, angry, scared? Then, try to identify where in your waking life were you feeling that way.
Hope that helps!