For me it's simply this:

Chan Heung - Founder of CLF
Jeung Yim - Founder of Hung Sing branch
Tam Sam - Founder of Buk Sing branch.

The co-founder theory doesn't hold water for me becuase where can you see Jeung Yim's mark on Chan Heung's style. If they "co-founded" the style there would be more crossover and similarity between the branches. What exactly was "co-founded"?

Both sides have holes in their histories the Choy Fook is Ching Cho thing on the Chan side and the Jeung Yim studied with Lay Yau San on the Hung Sing side.