id like to message the users on my 2012 server

hello
im running 4 servers on win 2012
im told it's the same as win8 (but my home computer runs on win7 so I dono)

I have about 60 RDP users on one server and I need 8 of them to move to another
id like to have them get a popup message every time they login
but only them not everyone
is there a way to do this ?


also from time to time I need to reboot the server and I would like to send a mass message in the server from task man
that worked really good in 2008 but in 2012 it will only let me message one user at a time
is there any fix for this ?

I have tried
if the server has been running for just a few min it works wonderfully
but if it's been running for a day or so it seems to do nothing at all
I have no idea why