1) You're certainly right about angels being able to think for themselves. I was suggesting they had no ability to make Moral decisions. Not that they cannot perform evil actions, as committing genocide is evil but angels have had such acts attributed to them, but they cannot make the decision to do so in any way which bears moral weight. The same way that bunny rabbit eats her own babies in a clearly horrific and evil act of infanticide but it means jack and diddly because the rabbit doesn't have the ability to question the good and evil of her actions. She does it because she must, as angels do evil or good because they must.
2) Angels and Demons would have the intellectual capacity to interact with people under this precept. Their inability to make decisions on a moral basis wouldn't hamper that. People who believe that they're always in the right, without any ability to self-reflect on their own culpability, independent of any moral consideration, still have kids, after all. We just generally recognize that they're self-centered jerks whose self-righteousness blinds them to the harm they do.
3) Indeed, a divine higher power would want beings acting on it's behalf using higher thought and rational, tactical, thought in order to achieve it's own will. But it wouldn't want them questioning it's authority/morality/etc since that could lead to disloyalty.
The Lucifer thing I don't wanna get into too deeply, 'cause religion, but... It's said he was able to rebel because he was specifically given free will where other angels weren't, and immediately used that gift to rebel, taking a third of the heavenly host with him. There's other interpretations, too, but that's a strong one to consider.