Thank you for your reply. I checked my state's estate tax requirement, and it begins at 4 million dollars of estate for 2018, and in 2019, will increase to the same as federal estate tax exemption which leads me to further questions.
1) Is it correct to say that as long as the estate during the year of parent's passing is below the estate tax requirement for both IRS and state, the estate is not subject to estate tax no matter how the estate was co-owned with the child?
2) If the child inherits parent's Traditional IRA, my understanding is inherited Traditional IRA will be subject to income tax, so should the Traditional IRA be excluded in estate tax consideration? It seems to me inherited Traditional IRA cannot be subject to both income tax and estate tax.
3) In case of inherited Roth IRA, will that be excluded from estate tax consideration? Money in Roth IRA has been already taxed so withdrawal is income-tax free for both the principal and earning so is it excluded from estate tax?