When needing to ring multiple extension and then go into an individual voicemail, it is best to use a Cascade Ring inside of transferring the calls to multiple extensions.
When using Cascade Ring, you can choose to ring multiple extensions and also ring the each extension that you are calling. For example, if you are calling extension 2000 and you also want to ring 2001 and 2002 at the same time, you can easily use a Cascade Ring to do so. By default, after the Cascade ring is complete the call will transfer to the voicemail for that extension.
When using a transfer to rule, the calls will not ring into voicemail and must be transferred to another destination to do so