@texczech82 We can only theorize, but Czech Wiktionary page says that the most probable explanation is the connection of čel- and -ch.
The exact meaning of čel is unknown, but words like člověk (human) and čeleď (family, tribe) are derivatives of the same word, so it could indeed mean family.
Today we (Czechs and Slovaks) use rodina for family, though čeleď (Slovak čeľaď) is a scientific term for family of animals and plants. Čeleď means family in [kingdom -> phylum -> class -> order -> suborder -> family -> genus -> species -> subspecies].
The meaning of suffix -ch is a member. So if čel means family, then čech means family member. The same goes for Valach, Kazach…
The Czech name for Bohemia is Čechy, which can be either a plural form of inanimate noun Čech or a toponym – a land inhabited by Čech people.