Two questions about DDMS.

I have problems with DDMS, I also watched your video and configured exactly everything as in your example, just use different radio IDs.
My radios send ARS messages, but the control station obviously does not send ACK. Is there anything else that needs to be configured in the control station configuration for it to send an ACK?

The three settings which are important on the radios are:

Admit Criteria on the Control Station must be set to Always. Setting this to channel free will prevent the radio from sending anything if there is any activity on the channel. In Capacity Plus systems you might need to set this to Color Code Free - that is okay too.

Data Call Confirmed must be enabled (ticked). If unticked, the radio will not send any acknowledgement for received data (this includes location, text and telemetry).

On the fielded radios, the ARS Radio ID must be the Radio ID of the Control Station. In other words, the Radio ID in the control station must match that in the ARS Radio ID of the other radios.

Additionally: how can I get DDMS to delete radios that have not been online for a while?

DDMS automatically purges presence data after a certain amount of time of no activity from that radio. This is defined by the DeregistrationTO setting in DDMS (Interfaces>>ARS Settings).