It makes me happy when someone wants to get informed about circumcision! Good for you.
My husband is circumcised. He never really thought much about it until we were going to have a baby together (my 2nd), and I told him the true facts about it. The foreskin has really important protective and sexual functions. His glans is calloused instead of smooth and supple like it should be, because it is no longer covered. Erections pull his skin very tight. He lost tens of thousands of nerve endings. We both lost the gliding action of the foreskin. His mother was told it had to be done, or he'd get cancer, which of course is not true. So he's not mad at her... she was uninformed back when he was born. It wasn't easy to get the information back then. But a lot was taken from him without his consent, and we both wish he had his foreskin.
And that is really the heart of it for both of us, now. Our children have a right to their whole bodies. We as their parents are their caretakers, and we don't have the right to alter their bodies for any kind of personal preference. Though honestly, now having seen my sons the way they were meant to be, the circumcised penis looks... naked to me! In a natural penis, the glans is covered unless the man is ready for sex- and yikes. I don't want to see my boys that way!
Here are a couple of sites to get you started: http://www.thewholenetwork.org/the-library.html
This is Dr. Momma's blog site: http://www.drmomma.org/2010/02/dr-dean-edell-statement-on-circumcision.html#uds-search-results For some reason I can't get the search function to work there, to come up with all of her posts about circumcision. But there is tons of excellent information on there (on circ and other topics), so please poke around and read some more.
And of course, there is MDC's own Case Against Circumcision forum. I would suggest going to the other sites and getting some research done, and then if you still have questions, go to CAC. You probably don't want to go in as a complete newbie, as some people complain that the regular posters there are so passionate about the cause as to be harsh to the uninformed. I don't think that is really true, so much as it can be hard for people who are just learning the truth to have this complete paradigm shift (what I thought was good is actually... bad? how can this be???)
The advice on siblings that's usually given in there is that you'd say something like "When you (ds1) were born, the doctors told us this was best for you. By the time ds2 came along, we had more information and decided it wasn't necessary." Personally if I had circumcised my son, I would give him information about restoring his foreskin, when he came of age.