Complex sentence: Walter was the heir to the earldom of Lennox and had been in open revolt against his father during 1423 for not giving way to his younger brother Alexander for this title and also disagreed with his father's acquiescence to the return of James to Scotland.
Split into simpler sentences: Walter was the heir to the earldom of Lennox and had been in open revolt against his father during 1423 for not giving way to his younger brother Alexander for this title. He also disagreed with his father's acquiescence to the return of James to Scotland.