I thought Cielo Drive was the former home of Terry Melcher, sometime producer for (and sometime member of) the Beach Boys.
Melcher thought Manson was not that great, and didn't want to work with him. We don't know what language Melcher used to communicate his lack of interest to Manson, but (knowing the LA music scene a little) he might have been fairly brutal in giving his verdict. There might have been a dope deal involved also, I think Manson was selling drugs to get by at the time, but I'm not sure.
By the time Manson's people turned up to murder everyone, Melcher had moved elsewhere; Roman Polanski was just one of a series of renters.
Regarding The LaBianca's though they lived in the Los Feliz district near Vermont Ave. This is several miles away. They were not connected to the music or Hollywood scene, to my knowledge, at least.