Mom has trust fund with Two sisters and brother handling it. Who files the incom

Mom is the sole beneficiary of a trust? Is the trust retaining current income or distributing it each year?

One possibility is that the trust distributes cap gains, dividends and interest, along with some principal. In that case the trustee creates a Schedule K and the tax on this distributed income is mom's, as if she had it in her name.

The other common possibility, is the trust retains earnings, and the trustee must file a return, nut just to report that it issued the Sch K, but to pay tax on those earnings.

Revocable: Interest goes on Mom's tax return (1040) Irrevocable: Trustee files tax return (1041)