I think that all 3 cool-downs should be separate and go in tiers of cool-down length.

For example: Skill one takes (18 seconds) to cool-down, Skill two takes (28 seconds) to cool-down, and skill three can stay at the (45 second) cool-down, seeing as skill three seems to be the most used on any sprite and the most powerful.

And when the skills are at independent cool-downs that means you can use skill one more often than skills two or three simply because its the weaker of the three and therefore should not be limited in use.

Granted i would like it to be that once a skill is activated you cant use the other skills while the one currently active is in effect.

Example: you cant use caustic quills from the maskeraith until the miasma cloud from skill three is finished, but once the effect has vanished you can again use caustic quills even if the miasma cloud from skill three is on cool-down.

This is a similar effect to what normal RPG games do with similar skills.