Have you discussed beneficiaries, and transfer of your grandmother's investments at end-of-life?
I know it's a sensitive subject, but a little planning can insure more of the wealth is inherited, rather than taxed away.
It might make sense to identify future beneficiaries NOW, and to set up separate IRA accounts for the benefit of these beneficiaries.
Normally, a child (or grand child) can NOT assume ownership of or roll over a parent's (grand-parent's) inherited IRA. However, the parent can create an IRA in the child's name for the benefit of the child. By doing so, the child can perform a trustee-to-trustee transfer from this IRA to her IRA after the IRA holder's death. By doing so, the child does not have to begin distributing the inherited assets any sooner than normally required of IRA owners.
If you don't, it's more complicated (and in my mind, something to avoid). Here's how it works: If you inherit an IRA from a parent and can't transfer it to your IRA, you might need to distribute the account by the end of a five-year period. The five-year rule applies if any of the beneficiaries is not an individual (ex; a company, charitable organization, etc). If all beneficiaries are individuals, you can stretch out required payments based on the life expectancy of the oldest beneficiary. If your parent designates separate accounts within an IRA, you can stretch out distributions of your portion of the inheritance over your life expectancy, not that of the oldest beneficiary. However, if you miss the deadline for the first distribution, which is December 31 of the year following your parent’s death, the five-year rule then applies.