Because these three members were the only ones that were nominated from the first thread.
http://www.forumkorner.org/thread-51795.html
To get nominated, someone has to nominate you for MOTM. There was a thread for this earlier this month.
http://www.forumkorner.org/thread-51795.html
As for your second question, I'm not sure what you mean.
But whenever someone votes in the poll, other member can see who voted for which member, so we'll know if someone voted for themselves.
There's also no prize for MOTM, as far as I'm concerned.