Is the husband sinful for installing a satellite dish for his wife after she threatened to go to her family's house, even though he did it unwillingly?

You are responsible for your wife, and it is not permissible for you to allow her to watch forbidden things. You must prevent her from doing so. Since you are the one in authority, it is incumbent upon you to change the evil with your hand as long as you are able to. Your wife's threat to go to her family's house does not absolve you of responsibility; rather, she would be disobedient (nashiz) by doing so, and she must be disciplined. You can refer the matter to a Sharia judge. Be keen on advising her, and seek help from the wise members of her family if possible.