When I was in elementary school (2000s), I read a book series about little people living in a normal-sized person's house (NOT "The Borrowers"). I actually have no idea when it was written, but it was probably later than the 1960s and earlier than the 2000s.
Mainly it was about the advetures of a family, where the father, who was tallest, was six inches tall. The nuclear family was just a mother, father, and a boy and a girl, but they also had an uncle and a cousin named Nick, who at some point in the series gets married. There are other communities of tiny people, including ones who live in the mountains and ones who live in a scrap yard. I think the uncle lived in the scrap yard at some point.
One of the books was about how two children from the mountains came to visit the scrap yard riding a crow with their parents when they were two, and somehow they got separated, and they ended up living with the scrap yard community, where they thought they were twins even though they were cousins. Later, they're reunited with their parents/aunt and uncle.
Also, Nick was the adventurous one,and I feel like he had a toy plane or something that he flew around in, but I feel like the normal people would notice, so that might be wrong.
Another thing: all the little people had tails (looked like dog tails), and the books mentioned how they were always careful to keep brushed and whatnot.
Lastly, I feel like there was some dangers or other with mice, and like how the uncle's pet mouse was the only one they weren't afraid of, or something, but I'm less certain about that bit.
While this was a chapter book, there were some black and white drawing in it.
(I remember all the random details but not the title. Go figure.)