Questions about the Breaking Bad script(Season2 episode12)

The scene where Walter and Jane's father in a bar counter, they were talking like:
Walter : So, any advice? Having a daughter.
Jane's father : Any advice? Not really. Just love them. Just I mean, they they are who they are.
Walter : I've got this nephew. This nephew who is I mean, he's an adult. But you can't infantilize them, you can't live their life for them. But still, I mean, there is that frustration.

Question1:
Why is Jane's father replying with plural form like "Just love them" or "they are who they are", even though Walter is using singular "a daughter" ?

Question2:
In the same way, Walter is using singular forms at first in the second script, like "this nephew", "he's an adult". Why does this singular turn plural like "you can't infantilize them".

Question3:
Walter is saying "But you can't infantilize them, you can't live their life for them". Who is "you"? people in general?Jane's father? If the former, can it be replaced to "we" ?

1/2 because they are talking generally about parents raising children. children is plural so them is plural. 

3 when talking generally and giving advice we say "you", which is actually both plural and singular (English doesnt have a plural form of you).

For example we have a saying "You can't be too careful"

"we" could be used but not in the context of giving advice