Whoi Is Online? And Database Lock

Hello,
I don't really know if this can be accomplished withing the asprunner but I will try:
I have 3 people(admins) who can add edit delete records to my database.

Each are assigned their unique user name and password.
what I would like to do is:

1. lock the database for editing/editing deleting for any other user while user1 is doing something in the database.
   
2. I would like other users(including guests it does not matter) to see who is currently online - so that if user2 wanted to add record and he can see that it is the user 3 who is currently in the database to call him and ask to "get out" <img src='https://asprunner.com/forums/file.php?topicimage=1&fieldname=question&id=20499&image=1&table=forumtopics' class='bbc_emoticon' alt=':)' />
   is it possible, if yes, please let me know how?
   
   Thank you