What to do if someone wants to renounce an inheritance?

I am so sorry for your loss. You need to seek help from an attorney in your are in order to confirm and execute what ever documents needed for this matter.  It is my understanding that Virginia does indeed allow a party to refuse to accept their inheritance.  It is called a "disclaimer" of inheritance.  It is my understanding that if the property in disclaimed then the fiduciary looks back to the original Will to see if it addresses the issue and that it is treated as if the refusing party has predeceased the decedent.  But the portion will most likey  be put back in to the pot, so to speak, to be distributed between the remaining siblings.  In order for your one sibling to give his or her  portion to the other sibling they may have to actually accept the inheritance then gift it over.  Good luck.