"
I believe I will deduct the full amount of attorney fees paid in 2017 that covered charges from 2015..."
That is fine provided the fees were actually paid in 2017 (you cannot deduct any fees paid in previous tax years).
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Do I Divide the new figure on Line 1041, Line 17 (U.S. Bond interest minus attorney fees) by 4...."
Yes. You essentially subtract the total fees paid from the total bond interest to arrive at the adjusted total income (that is entered on Line 17) and then the remainder is split four ways.
"Attorney fees were NOT subtracted from the amount the beneficiary's received in 2017."
That is irrelevant. The beneficiaries will report the amount on their K-1s, which is their share of the interest income less expenses (fees) reported by the estate on the 1041. Any excess they received is simply a distribution of the corpus (principal) of the estate and is not taxable.
