Complex sentence: His brother-in-law Ralph Neville remained one of his strongest supporters, and so did his eldest half-brother John Beaufort, even though Henry revoked Richard II's grant to John of a marquessate.
Split into simpler sentences: His brother-in-law, Ralph Neville, remained one of his strongest supporters. So did his eldest half-brother, John Beaufort, even though Henry revoked Richard II's grant to John of a marquessate.