Another post about conjoined twins

I know we have had a couple posts now about conjoined twins, but reading them has caused to me to ask some further questions. Some people debated about getting the surgery, but I would be interested to know in what percentage continue to live as two, and from that how their lives function "normally." Also I would interested to know in the life span of conjoined twins. While some seem as if they live quality lives, I'm sure they're pairs that are riddled with medical conditions. As I commented on an earlier post, it seems like a medical miracle for two hearts, two brains, four lungs to all be functioning properly. Especially if organs are shared. More than anything the physiology of the conjoined twin seems to be the most interesting to me. Please do not view this in a negative light, because the physiology of the human is intricate itself. It would just seem that when organs are doubled, this becomes  more complex.