I'm so sorry that you are having these problems. I would suggest that as far as the dad is concerned that maybe you could start the conversations, and remember it is ok to just ride in the car without talking sometimes. Please try to be open with your family and discuss these things freely. If you do talk about these things with your family it will make you more of a member of the family. Because family members discuss their problems with one another.
As for the sister, you should treat her as if she was your real sister. It is ok to argue and fight with your sister. I have three boys and at least two of them have an arguement everyday. Please don't hold in your issues. Talk about them with the family members.
And last but not least, dont become involved in the neighborhood unless your host parents tell you that it is ok. Please discuss this with your host mom. There might be people that your host mom is uncomfortable allowing you to socialize with. Your safety is the most important thing.
How are you doing in school? Do you have friends that you can go to games with or have over for the weekend? Make some friends that you can invite to your house. Get permission from your host mom before inviting anyone over.
Take care and let me know how things are going,
Aendert das was an der Tatsache, dass vielleicht die Chemie ueberhaupt nicht stimmt, ich hab doch schon sooo oft versucht mit ihm zu reden!