AR 600-20 also contains information on the structure of rank and how it works.
Bottom-line: If you have been appointed as squad leader by the chain of command you have the authority to do what is required to execute your duties. You can counsel those Soldiers you outrank. If a soldier outranks you by time in grade, refer this matter to your platoon sergeant. It would be best for another individual to counsel this Soldier until you achieve promotable status. I also suggest you ask the platoon sergeant to review your counseling statements prior to showing them to your Soldiers.