I don't think Källa and
Kjell are related.
Kjell is a common Swedish name. Källa is extremely uncommon, but there is an actress called Källa Bie (I think her parents were a bit "hippiesque", because her brothers are called Nanok and Loa) which I guess have inspired some parents.
Snöfrid is pronounced something like SNEW-freed (the Ö sounds more like eu in the French word "adieu").