Trust taxes

Were the proceeds from the IRA rolled over to an inherited IRA?  If it was not converted to an inherited IRA then the distribution was a taxable event and the trust will have to either pay tax on the distribution or distribute the funds to the beneficiaries who will have to pay tax on the distribution. 

If the proceeds were transferred to an inherited IRA, then the type of trust will determine the distribution period.  If the trust qualifies as a "see-through" trust distributions must be taken within five years of the death of your father, or if he had already reached the beginning date for required minimum distributions (RMDs) can be taken over your father's remaining life expectancy (your father still has a life expectancy under IRS tables even though he passed away).

Under the Secure Act, trusts that do not qualify as “see-through” trusts — vehicles by which individuals pass retirement assets to beneficiaries — they must take distributions within five years of an account owner’s death, or if the account owner had already reached their required beginning date, minimum required distributions (RMDs) can be taken over the deceased account owner’s remaining life expectancy.1 Conversely, beneficiaries of a see-through trust may be able to take distributions based upon the 10-year rule or, in limited situations, over the life expectancy of individual trust beneficiaries. 

If the trust qualifies as a see-through trust the beneficiaries may be able to take distributions based upon the 10-year rule or, in limited situations, over the life expectancy of individual trust beneficiaries. 

I recommend you consult with an estate planning attorney.