A period/full stop, and the key next to it, a comma
Live on the next row up of the keyboard. The first identical twins are the colon, living with (on the same key as) the semicolon (the fraternal twins). Depending on your keyboard, the key next to that has either " and ' or @ and ' - presumably you have the former, making the identical twins quotation marks, and their little sister an apostrophe.
Is the other period/full stop over by the numpad, out on the outskirts of the keyboard