Regarding Shevet Shimon, it states in Divrei Hayamim that when David became king he made Shimon leave Yehudah’s territory because Yehudah needed the space. (little known fact)
Although they originally were together, it did not remain that way.
Also, the pesukim in Milachim 1 clearly state that Achiya Hashiloni told Yeravam that Hashem said that He would take away ten tribes from Shlomo’s son. He ripped his new garment into twelve pieces (or twelve cuts – see mitzodos) and gave Yaravam 10, keeping two. Which represented Yehudah and Binyamin.
Also, they are always referred (correctly) as the ten tribes. The mishnah in Sandhedrin calls them the aseres hashvatim. Shimeon was part of the ten.