Federal Estate Tax: If your stepfather’s estate is valued at more than $675,000, then the executor or other administrator of the estate must file Form 706, the federal estate tax return (IRC section 6018(a)). If the estate is valued at less than that, there is no return to file. However, even if a return must be filed, there will be no tax because there is Marital Deduction allowed for all property passing to your mother. If you need to file form 706, you can download it for free at:
http://www.irs.ustreas.gov/forms_pubs/index.html.
As for the state of Louisiana, a return may have to be filed depending on the size of the estate, but I doubt that there will be any tax required because of the marital deduction; however, there may be.:
LRS-47:2425 requires that an inheritance tax return be filed by or on behalf of the heirs and legatees of a decedent in any case where inheritance tax is due or where the gross value of the deceased's estate is $15,000.00 or more. LRS- 47:2436 requires that an estate transfer tax return be filed by or on behalf of the heirs or legatees in every case where estate transfer tax is due or where the value of the deceased's net estate is $60,000.00 or more. LRS-47:2425(B) requires that the return be filed within nine months after death of a decedent.
The following Louisiana forms can be downloaded at
http://www.rev.state.la.us/htmlfiles/tax_forms/tax_forms.asp#InheritanceandGiftTaxes:
R-3318 Inheritance and Estate Transfer Tax Return
R-3318i Inheritance and Estate Transfer Tax Return Instructions