Complex sentence: Matthijs Dulken, a seasoned and wily commander, was head of Spanish occupied Grol and had available to him 1200 foot soldiers (not accounting enlisted citizens) and around 100 cavalry, commanded by Lambert Verreyken.
Split into simpler sentences: Matthijs Dulken, a seasoned and wily commander, was the head of the Spanish army occupying Grol. He had available to him 1200 foot soldiers (not accounting enlisted citizens) and around 100 cavalry, commanded by Lambert Verreyken.