If you were the designated beneficiary of your wife's IRA, yes, this is taxable income to you and must be reported on your tax return. The will has no bearing on this because this is not part of the probate estate.
Whatever you gave to her children are gifts from you to her children and have nothing to due with your wife's estate. You must file a 2018 Form 709 Gift Tax return if your gifts to any one person in 2018 exceeded $15,000.
