OK...let me try.
As for #1, I think "please" here is similar in meaning to "like". ( "to behave...' is the object of the verb 'please', I reckon. I'm not used to this usage, actually.) And "unless" is, as you know, is similar in meaning to "if...not".
So, if I rewrite that part, it goes like this:
"Do not have the absurdly wrong idea that you can do as you like/whatever you want at home, if you don't like to behave in a perfectly gentlemanly or ladylike manner."
As for #2, both work in my opinion.
As for #3, let's think about how something/somebody becomes sacred. If you have a great respect and affection for something/somebody, it (s/he) will eventually become sacred, right? If you are a religious person, I think you'll understand what I mean. Therefore I'd go for the latter - "each member of the family"
My interpretation might be wrong.
Please wait for other teachers to reply.