The meanings are
A. not any member of our group (i.e. no person among those in our group)
{not one} {of us}
We are, none of us, perfect.
We are, not one of us, perfect.
There is, none of us, but has some flaw in his character.
There is, not one of us, but has some flaw in his character.
B. not a member of our group (i.e. does not belong to our group)
{not} {one of us}
He is from another (country, tribe, group, clan, county, ... whatever). He's not one of us.
In the 18th c. and earlier, "none of us" could be used to mean "not one of us", not a member of our group, and the usage has survived in regional dialects.
A stranger, he is. He's none of us.