How to prevent users messaging users of thier own role

My requirement:
I have 2 roles Role 1 and Role 2
2.1.Role 2 can write message and read message from Role1 referring a content of Role 1(Link on the content)
3.Role1 Can Read and reply to a message of Role2
4.Role1 or Role2 Cannot write direct messages to each other
5.Role2 Can only reference a content and message and cannot write direct message
6.Users of Role1 or Role 2 Cannot write message to user of same Role
7.Not permitted as per permission of user name/id should not be searched in auto complete in To: field

Currently my settings
under user Permissions-

Private messages-
Read private messages Role 1 Role 2
Write Private messages - Role 2

Privatemsg roles-
Write private messages to role 1 - - Role 2
Write private messages to role 2 - -

1.This setting is not preventing the users from writing direct messages to same role
2.This not preventing Role 2 to write a direct message to Role1
3.all user/ids show up in To:field