I don't know about that ...Wario Ware is definitely a spin-off of a spin-off. But ... I don't consider DKC a spin-off. It's a completely different direction from Mario games, considering the only participation DK ever had was as a villain that throws barrels.
DK Jr was a spin-off, because it was similar enough to the original Mario Bros, but DKC took an entire different direction, invented its own universe and everything. Mario doesn't even exist, so I don't know if I'd consider it a spin-off.
Although, I don't know the criteria we're using, so maybe using a different definition, you're right.