Complex sentence: George quarreled violently with Richard (which Poirot and Entwhistle learn from Lanscombe), and in his disgust even forged a will for Richard, disinheriting himself in favor of the other relatives.
Split into simpler sentences: George quarreled violently with Richard (which Poirot and Entwhistle learn from Lanscombe). George even forged a will for Richard, disinheriting himself in favor of the other relatives.