Complex sentence: He instead stayed at Wimborne together with his men and a kidnapped nun, seemingly preparing for a long stand-off, although it appears he had the resources for a frontal assault and was preparing to attack when he rode north during the night.
Split into simpler sentences: He instead stayed within Wimborne with his men and a nun he had kidnapped, seemingly preparing for a long stand-off. However, Edward had the resources for a frontal assault and was preparing to make the attack when Æthelwold rode North in the night.