LH-20 is mixed mode, a combination of size exclusion and adsorption chromatography. That makes it somewhat difficult to "strategize" a method.
I would choose the least polar solvent system your mixture is soluble within, and run that solvent. Most sesquiterpenes are non-polar (there are exceptions) and these should elute faster with a less polar system than more polar compounds, the molecular size being roughly equal.
I have already done a separation on Silica gel and two compounds remain coeluted. That's why I was thinking about sephadex. I don't have also a HPLC at the lab.