For our boys we chose Dp sister and her husband because they are very simialar to us as far as parenting goes and what we all believe is best for the kids and they would teach them the same thing we would if anything happened to me and dp.
For Nick we also chose dp's best friend because dp knows that he will also teach him the things that we would.
For Ryan we chose another one of dp's close friends and his fiancee because they are very family orientated and have good values.