I have actually been through similar situations with my parents and my grandparents, and it was in reference to a lot of abuse. First off, I highly agree with not expecting anything from them whatsoever. It is my hope that they will not point fingers at you, but be aware that that is a realistic possibility. I think the key thing to keep in mind is that while you are saying what you need to, to your parents, that this is actually about YOU and NOT them. They essentially have nothing to do with this equation other than being there to hear what you have to say. In that same vein I have heard countless times in therapy and group therapy that whenever confronting anyone, or even simply communicating with someone it is vital to use "I" statements. E.g. I feel such and such. This event occurred and as a result I feel this or that. Try to stay away from any "You" statements such as you make me feel this, etc...
I think writing down what you need to say is a very good idea. Not only will it help you to not forget anything, but it also gives you a chance to hone in on how you want to say things, PLUS writing it down period will prove very theraputic and with that kind of preparation the actual conversation will indeed feel much more like closure. Remember, this is about you. So say everything you need to so that when finished you can truly be done and begin the healing process. YOU can be done. They probably won't be, and that's fine and to be expected.
Were they in a place to be receptive or truly and earnestly consider you and your feelings about the matter than most likely the abuse would not have occured in the first place, or they would've themselves addressed the issues in the past.
I truly do not mean to come across as a negative nelly, because in all reality this is SO incredibly healthy and you are to be comended and feel very, very proud of yourself for choosing to take this step. It shows courage, strength and an earnest desire to be healthy and happy. There are so many people who deny and/or ignore issues like this. So give yourself lots and lots of pats on the back. I know it sounds kinda funny, but it really does work, tell yourself how much you love yourself. Even a simple Cognac, I love you. It is very helpful.
You also mentioned your brothers. If confronting your parents all together I would also recommend doing a couple rehearsals or run throughs if you will. There will be a lot of strong emotions in that room and you three need to be a united front. If one deviates from the intent of the conversation it could make things more difficult on the other siblings. Again remember, this is about you three, not your parents.
Now as far as the religion aspect goes, what is said about that and how much is obviously all your choice and discretion. I would advise to tread lightly in that area because while yes it is very much related and intertwined (my situation was the same, so I understand how much of a muddled ball sh*t it feels like) you are addressing them about abuse, which JW or not, would still have been an issue. The organization did not make them or motivate them to do this, instead it enabled them to go unpunished and remain unaccountable to the rest of the world for it. It's a fine line, but it is still a line.
We ALL know how defensive "faithful" JW's get. They will already be on guard as people and as parents and tipping the hat too far in the direction of religion could prove to be the straw that breaks the camels back. Also, and this has happened to me, remarks and issues stated about the religion can be used as a tool to discredit your issues with abuse, and just as it is very much intertwined for you, it can be used as a related issue against you, and very easily transformed into a huge finger to point back at you. E.g. If you were more faithful and had a better relationship with Jehovah you would better understand how your father could be re-appointed and any and all past sins forgiven in the spirit of heartfelt repentance, etc. etc. I can really see that backfiring. So, all I'm saying (and I apologize because I know I'm rambling) is to step lightly and really think about how much you want to go into that. Which again, the writing things down prior to and re-hearsing with your siblings will really help.
And if your siblings aren't on the same page but you feel solid about your approach or what you want to say, than know and trust that you yourself have the strength to do this on your own. You DO. Even if you don't believe it right this moment, you keep drilling that into your head, and when the moment comes you will be amazed at the amount of strength you have buried inside.
I know it feels like a huge mountain right now, and it is in a way. But the thing to keep in mind is you are not a little kid trying to climb Mt. Everest. You a grown adult with absolutely the best of intentions who has already climbed mountains, bigger than this one, you just didn't realize until you were done. So this is nothing you can't do, and nothing harder than things you've done already. So, without sounding too crude, go kick that mountain in the balls.