Can dependents travel and renew their visas separately on a dependent visa (DTV) in Thailand?

Traveling separately is ok. Extending (as in getting 180 days more on the same entry) separately is likely to cause issues. There has been at least one report of a dependent who could not extend their stay at the immigration office, because the main visa holder had been out of the country (without their dependent) and could not extend their permit to stay themselves (too early to apply for an extension). I cannot remember which office it was, but they definitely insisted on the main visa holder applying for an extension too, in order for the dependent to be able to apply for one themselves.

to answer your question about if the DTV's (primary / dependent) are thai'd 😮 err tied together that answer is NO

you can come and go separately once they're issued.. You don't have to travel together

The DTV will require evidence of managing the property online. You can travel independently. Joint bank account is most likely ok but you should double check with the embassy you are applying from.

Just leasing out a property is unlikely to be enough, you need to show that you manage the property. Joint bank account might be ok depending on the consulate but usually requires double the money in it. Yes you can travel separately but if getting an extension inside Thailand you might have an issue unless both extend