Ya gotta do it. If you don't it will eat at you. You most likely not like what you see, what you hear and will walk away with more questions than you will ever have answers for, but you have to do it.
If you don't, then you will never have closure.
I think you're going into it with the right mindset. Some people are looking for that 'brady bunch' experience, and are always let down. I have had many people in my life, friends, family etc that have dealt with what you are dealing with. It ain't easy, but may be cathartic.
You should approach it with some clear goals in mind. Such as what is your reason for approaching him/them, to get it off your chest, to confront him as to his behavior, to re-connect....something like that. Then let the meeting satisfy those goals, ya'know? This is a logical approach, and can help to remove some of the emotion.
It was mentioned in here that our parents 'did the best they could'. Maybe thats the truth, I don't know. In this day and age, there are so many avenues for education, or resources that our parents could have utilized, it is easy (for me) to see that they are selfish and don't fucking care.
I don't know if this helps, but this is one Hippie's suggestion.
luck to you my friend~