Complex sentence: They have only one Chief Sardar whose name is Sardar Muhammad Khan Noohani but now Chief Sardar Muhammad Khan is a very old man and has selected his last son Sardar Hakim Khan Noohani as the Chief Sardar.
Split into simpler sentences: They have only one Chief Sardar, whose name is Sardar Muhammad Khan Noohani. However, Chief Sardar Muhammad Khan is a very old man and has selected his last son Sardar Hakim Khan Noohani as the Chief Sardar.