Complex sentence: Most of highest-classed kuge belonged to the Fujiwara clan and Minamoto clan, but there were still other clans like the Sugawara clan, the Kiyohara clan, and the Ōe clan.
Split into simpler sentences: Most of highest classed kuge belonged to the Fujiwara clan and Minamoto clan. But there were still other clans like the Sugawara clan, the Kiyohara clan and the Ōe clan.