Use lecithin to emulsify the oils. Otherwise, they just rise to surface of the container.
Lecithin is obtainable at health food stores, and on the nutritional supplement aisle of many other stores.
I blend mine to really, really fine powder, typically from the store it is coarse-crumbly.
I suspect lecithin would spoil on storage, so I mix small batches, and use within a week.
Lecithin has a fat-soluble end of the molecule, and a polar end that absorbs/attaches to water. It bridges oil to water mixtures.
The menthol/thymol dominated oils are likely interchangeable, as the effect on internal mites is likely the desired action. Eucalyptus oil is often the cheapest, followed by tea-tree. The lemon-grass oil has a pheromone function. Rose-geranium, lemon balm, lemon verbena can be substituted for lemon grass.