Assuming you rolled over the 401k money to a traditional IRA, any distributions will add to your taxable income (the alimony). You will have to contact the custodian (Vanguard) to request a distribution. If there is not enough cash in the account, you will have to sell some of the investments.
If you are under 59 1/2, then there will be a 10% penalty (additional tax) on any amounts you withdraw.
The income taxes you will pay depend on your filing status, exemptions and deductions. Do you claim your parents as dependents? Do you file Single or Head of Household?
How much money do you estimate you'll withdraw this year?
Sorry to hear you about your dad. Hope he's OK.
So, if you are Single with no dependents, your gross income for this year would be the alimony plus the retirement distribution or $41,000. Assuming you take the standard deduction and do not claim any tax credits, then the income tax on the $20,000 withdrawal will be 15% plus the 10% penalty for a total of $5,000.