As an admin, I deleted first all the members of the group, left it and then deleted the group. Can the other members still see the messages?
Yes they can see all those messages, you can see the example here: Example Conversation for those who has been removed from the WhatsApp group. So removing people from the group is not the best way to hide messages.
It is possible for them to read the messages of the group if they were using the previous version of WhatsApp.
With the latest update of WhatsApp, if you delete all messages you send with option
delete for everyone, your messages will not be visible anymore to any member.
But as you are asking that on first removing each member of the group, then delete the group will not show anyone anyhow the existence of the group.
For more information, check this post out.
Yes, in your case the members of the group will still see the messages.
Removing someone from a group will not delete the messages off of their phone.
Deleting a group on your phone after exiting it, will only delete the message off of your phone and no-one else's.
The only thing you could have done before deleting the group was, delete the messages that you have posted in the past 7 min. (Or 5-6 days) off of the participants phone, by long pressing on the messages>delete>'delete for everyone'.