If the estate income is applied to satisfy the legacies, as the widow will have a right to that income will this not amount to a loan from her to the trustees? I do not believe it will prevent her from being treated as receiving the income for income tax purposes.
From the expiry of the executor’s year, the legatees will be entitled to interest on their legacies. Any payment to them will first be treated as settlement of the interest then accrued, before reducing the amount of the legacy outstanding. This could cause administrative nightmares.
One possibility might be to have an interest only loan secured on the trust property(s) so that the legacies can be paid. The interest on the loan, though, would be payable by the life tenant (whose entitlement would be reduced by interest on the legacies in any event).
An alternative may be for the legatees to agree to payment being delayed until any of the properties are sold, although they might not be happy with the thought of the legacies being paid at some unknown future date (and perhaps not even during their lifetime!)