Julie, I'm so sorry. I recently went through this with my SIL (thankfully they had a girl).
When she said they would circ a boy, I reminded her that they don't HAVE to, that it is simply cosmetic surgery. I said "You hope and pray for 9 months to have a healthy, perfect baby that doesn't require any invasive medical treatment. If you're lucky enough to get that, why would you want to sign your baby up for elective surgery?"
I think most people don't really understand that it IS an operation, not "just a snip".
It didn't look as though I was going to talk her out of it that easily, so I said "OK, if you insist on having this done, at least make sure you know something about it first.
Make sure the baby first gets EMLA cream, and that they wait long enough for it to take effect. Then make sure he gets either a dorsal penile nerck block or a ring block, and make sure they wait long enough for THAT to take effect. Of course that doesn't eliminate the pain, it only reduces it, so have plenty of infant Tylenol on hand. Be sure to be with your baby the whole time, because he's going to be scared and in pain, and he'll need his Mommy, especially when they tear his foreskin from the glans.
After the surgery, keep a close watch for infection and bleeding. Babies can't tolerate very much blood loss, so even a little bleeding can be too much.
Most doctors today try to perform a "loose" circumcision, to leave enough foreskin for the boy to grow into. This remaining foreskin often tries to re-heal itself back onto the glans, forming adhesion. Usually these are not a problem and should be left alone to resolve themselves (which may take months or years). If adhesions form along the scar line, he may need another operation to fix them. Watch closely for signs of meatal stenosis, which is a narrowing of the opening to the urethra, caused by irritation, since the foreskin is no longer there to protect the glans. If it is severe enough to restrict urine flow, he may need another operation to correct it."
Hopefully, by this time she will realize that maybe she doesn't know as much about the operation as she should, and will either ask questions or run screaming for the phone to cancel the appointment!
Good luck to you, and please remember, evevn if they DO decide to circ you nephew, you will know that you did everything that you could do to stop it - and to make sure that he got the best possible pain relief.