Who are "Nevalim"?
Rashi: They are fools.
Radak: They are lowly, disgraced people, like "k'Echad ha'Nevalim" (Shmuel II, 13:13), "k'Achas ha'Nevalos" (Iyov 2:10). Targum Yonasan there is 'like one of the fools'; also here, he translated 'who are crazy.'
Malbim: Conditions for a Navi are (a) He attains true Nevu'ah. (b) The purpose of his Nevu'ah is to fix the nation (refer to 13:4:1:3). These Nevi'im are Nevalim ? Hashem did not speak to them. A true Navi gets Nevu'ah via Ru'ach Hashem that takes effect on him and speaks in him. These false Nevi'im follow their Ru'ach (refer to 12:3:2:2), or they saw great visions ? this is why they are called Ro'im, Chozim and Tzofin. However, they did not did not see anything!
What is "Rucham"?
Rashi: It is their desire.
Malbim: It is their imagination.
