The answer to your question is that you do not need to worry about ordering in-text citations at all because Mendeley does it or does not do it depending on the reference system that you adopt.
For instance, if you are using APA 6th edition referencing, Mendeley orders the in-text citations alphabetically because that is what APA requires. Or, if you are using the Harvard reference system, Mendeley orders the in-text citations chronologically because that is what the Harvard system requires.