Interesting… this is the third time this question or a variant of it has been asked in the last two weeks. I’m tired right now, so I’m just going to refer you to one of the other threads and then you could ask more questions if that doesn’t help.
But the short answer is you can either use a battery powered Device, and there are a couple of dozen that can work with SmartThings, or you can use a mains powered accessory switch, but it has to be a switch which actually has a radio that communicates directly to the SmartThings hub. Some do, but some add on switches, such as the GE brand, communicate with their own masters via physical traveler wire and those won’t work the way you want. But any of the battery powered devices would.
Anyway, take a look at these threads ( this is a clickable link)
This first one discusses a number of the battery operated options for this kind of use case:
And this one is talking about a mains powered device like the accessory switches
Either could work for your use case, so it just depends on what you prefer. In all cases, the switch will send a message to the hub and then the hub will send the messages to the other dimmer switches so they don’t all have to be on the same circuit. 
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