What are my dimmer options in this switch configuration?
This is a plain old &quot;bootleg 3-way&quot;.
What happened is the installer got cheap and used /2 when they should have used /3.  For neutral, they are simply bootlegging neutral off of ground.
This is completely illegal and it cannot continue in this configuration.
Unless you're willing to rewire all these cable runs, you're going to have to get pretty innovative to rescue this one.
Generally it looks like you'll need to re-task both former travelers to be actual always-hot and neutral, except at the very last location before the light.  That will be a smart switch &quot;master&quot;.  The others will be smart-switch &quot;remotes&quot; and you will need to choose products appropriately.
What's more alarming is you may have a houseful of this kind of stuff, and a fair amount of work ahead of you.  This stuff is dangerous and should be corrected ASAP.