"My family and I are going to a Shanghainese restaurant for lunch this weekend."
Since it hasn't happened yet, I think throwing a 要 or 会 in there would make the sentence flow better. Also, since it's not a specific restaurant, putting a 一家 before 上海饭馆 might work (oh, but then it'd sound redundant). Finally, there should be a 我的 before 家人 if I'm not mistaken. Like so: 这个周末我和 [我的] 家人 [会] 去 [一家] 上海饭馆吃午饭。