I think you are being nice (which is not a bad thiing!) in trying to keep this win/win for everyone and somehow resolve this with no bruised egos and ruffling as few feathers as possible.
Hopefully the advice others have given you has helped you reach such a goal.
As for me, maybe I did too much ENFP scanning (as opposed to 'reading') but I still don't get why you want to avoid a huge massive row. Aside from the fact you think this will NOT change the ENTJ minds... do you even have to change their minds?' Would a huge massive row really be such a bad thing if it shook things up enough to restructure/reorganize your fraternity for the better?
You said you had been 'appointed' the leader of the resistance because there are people who agree with you but are too scared to come forward?
You know, a whole herd of sheep can run over a lion. Or 3 of them.
Was that a good analogy?
Basically, if the majority of the organization comes out and says 'yay' or 'nay' can these 3 ENTJ's override them?
I hope everything turns out well. Also maybe not so helpful to hear but for all your planning when it comes down to the wire, it may end up you have to decide what is more important to you: this ENFP's continued membership and the principle of it or the goodwill of these ENTJ's and the appearance of harmony -- split decision time.
Do you have a plan b) for if peaceful resolution with ENTJ's is not possible? Because your true ultimate goal is to have the ENFP stay in the organizatino, ENTJ's be damned, correct? So if all else fails, will you turn into a vindicative, evil ISTP shadow?? Ooh, cause I wanna watch!