How can I use the same sheet in 2 different tabs?

Detail layouts are tied to sheets. The only time that isn’t the case is when you are at the top level of a tab or a link to screen. If you need two separate layouts from the same sheet, you will either need to duplicate the sheet, or use a custom action on the list to first set a user specific value, and then set conditions on the components you want to view, based on that condition.