AbaThembu are not a section of amaXhosa. They arrived in the Eastern Cape years before amaXhosa and their family trees are totally different. The reason why abaThembu are misconstrued as amaXhosa is due to their proximity to them. Also they speak the same language, viz., isiXhosa. This came about due to the first introduction of amaXhosa to reading and writing and the language the people spoke was then called isiXhosa. AmaNdungwane are, strictly speaking, also not amaHala as they are not descendants of Hala. Ndungwane was the first son of King Nxeko (in the Right hand House, I think), whose senior son was uHlanga. The majority of abaThembu were not disposed to having uHlanga as their king, and opted for his younger brother uDlomo. This is a long story, but to cut it short, Ndungwane sided with Dlomo in his subsequent battle with Nxeko. AmaNdungwane became a separate clan from that moment on. I hope this will embellish your website.
Velile Somana (Aa! Jongisizwe) of Nikelo of Mdunyelwa of Somana of Maphasa of Bawana of Tshatshu of Xhoba of Tukwa of Mawose of Dlomo of Nxeko (AV Somana is the author of Inguqu Ukuba Bendinini [ISBN: 9780947437954], currently a set-book for Grade 11 isiXhosa)