Of course you don’t need DTV holder’s stamp if main applicant is applying at the same time. Your case was in-person application and Jakarta was probably less strict, that’s why they didn’t ask 500K statement for dependent. For online e-visa, dependent applicant has to upload 500 K bank statement mandatory as well. Me and my wife just received DTV and dependent visa from Hanoi last week, they don’t allow walk-in applications anymore.
yes, dependent also needs to have 500K in their account or you can show main DTV holder account that has 500K additional for each dependent’s application.
They switched to an online application for everyone. However, you need to submit a scanned copy of the entry stamp from Cambodia to be eligible to apply at the Thai embassy in Cambodia.