Does more than one Cast When Damage Taken gem work?

Basically I was hoping to run more than one CWDT gem with molten shell in each of them, one of them would have a higher leveled CwDT and the other would be level 1 for more frequent proc's.. I understand that there is a global cooldown on CwDT which prevents both from casting at the same time, however, I am hoping this would just mean that the level 1 CwDT would proc frequently and every now and then I would get the higher level CwDT proc for more effectiveness. ? Thanks in advance.

The cooldown is not on CwDT, it's on Molten Shell (or whatever else you're supporting). Support gems can't have cooldowns. I know it sounds nitpicky but it's actually pretty crucial to understanding how the gem works.

Basically, it works fine for what you want. Whenever the low level Molten Shell triggers both go on cooldown. During the cooldown neither Molten Shell will track damage towards triggering, which means the higher one won't try to trigger when it's on cooldown unless the same hit triggers both of them at once. For that case, just make sure the higher level one comes first in trigger order.