Bob killed Lennon ,but Lennon knew who Red John is ... Before killing him ,he asked does he recognize his face... he said no.... so no Bob nor his brother are Red John...

Also , i don't think red john ,if he is a person ,is someone out of list... that would be disappointing for viewers ...

 For me there is only 2 suspects Roy and Chief ...
Chief for because he scared of bird on the roof...
And Roy because he like teresa and his walking ...

That scene when teresa is in hospital and nurse came in by error looking someone else, is very suspicious to me...

I think there was another similar moment when someone enter in the interrogation room by error ...
There is something in that scenes....