Are the [JW leadership / organization] really false prophets?
No. They're just an organization that claim to be spirit-directed; claim that God directs his people through them; and regularly refer to their own extra-biblical policies and instructions as being Jehovah's instructions and direction. (compare Deuteronomy 18:20a) They also equate leaving the org. with leaving Jehovah and they claim to be Jehovah's channel. They have also made several date predictions for the end of the world and predicted in the Awake magazine mission statement, for many years, that the generation that saw the events of 1914 will not pass away before the new world - this prediction they referred to as "the Creator's promise". But that was not tantamount to making a prediction in God's name, no, no, no. (compare Deuteronomy 18:22; Luke 21:8)
Obviously, all that I've said above does not match in any way, shape or fashion the definition and functions of one who acts as a prophet of God. Because quite unlike what I've described above, a prophet of God is one who is directed by God's spirit and is used by God to direct his people. Such a person will issue directions to the people while referring to such directions as coming from God. Often, prophets would also make predictions of future events, referring to such predictions as coming from the Creator, Jehovah. See, this is very , very, very different from the role of the JW organization mentioned above. lol.
And just because the founder of the organization, C.T. Russel published a volume of Studies in the Scriptures, filled with false apocalyptic date predictions, entitled: "The Time is at Hand!", that in no way, shape or fashion means that Jesus' warning at Luke 21:8 applies to him and his organization:
"And he said, “See that you are not led astray. For many will come in my name, saying, ‘I am he!’ and, ‘The time is at hand!’ Do not go after them." - Luke 21:8