Belgarath is right. The assets that the father inherited are subject to the beneficiary RMD rules- not the RMD rules that apply to the retirement account owner ( the son). Therefore, if the son died before the RBD, and the father is subject to the five year rule, he need not distribute any amount until the end of the five year period.
By the way, was this a sole proprietorship by any chance? ... If the business owner was a sole proprietor, then it may mean that the plan becomes an orphan plan upon his death…which would mean that the assets should be distributed as soon as possible after his death see the thread at
http://benefitslink.com/boards/index.php?s...t=0entry76127