The 1041 Estate is for the income of your father's estate after death until distributions are made.
It is possible that no 1041 will need to be filed.
From the question, it appears that there is a retirement account and when this is distributed to the heirs, they will each get a 1099R when distributions are made to them. The exception would be if the Estate takes the distributions and pays the taxes on it.
the Estate 1041 can be on a fiscal year, so if the year ends anytime in 2018, it would go on the beneficiaries 2018 income tax returns if a K-1 is generated by the Estate.
I would advise you to consult with the Atty that is handling the Estate.
