Complex sentence: Their initial reception was unpromising, both the MacLeods and MacDonalds advising Charles to return to France; they were eventually persuaded, the turning point being the commitment of the powerful and influential Donald Cameron of Lochiel.
Split into simpler sentences: Their initial reception was unpromising, both the MacLeods and MacDonalds advising Charles to return to France. They were eventually persuaded but the turning point was the commitment of the powerful and influential Donald Cameron of Lochiel.