Citation Placement - Turabian 9, 16.3.2 Referencing Notes in Text
The notation should be placed at the end of the sentence, after the final punctuation. Allow the word processor to pick the next number. Don't try to change the built in numbering, it will lead to problems. If the one notation relates to more than one citation, that is fine, just put them in the same order as the reference page and separate them with semicolons.