To me... the definition of being rude is attacking someone with words/ tone/ actions instead of your body. So, to me, very little of the above is rude. (The disregarding requests to stop anything... aka 'Stop touching me' and still touching someone is rude... but nothing else is.
Why?
Daughter =
1) Inviting someone whom she feels will already be there is a way of maintaining control (if he's going to come, I'd rather invite him and avoid the awkwardness of him just showing up) OR is BEING polite (not wanting him left out), OR BEING polite in offering to invite a friend of her brothers so he can have a friend there and not feel left out. All 3 options that spring to mind are actually VERY considerate of other people, and very unselfish.
2) She was asking you about things / bouncing things off of you... which is seeking guidence. Which is also neither rude nor impolite. Even if she's doing it with a lot of 'face saving' harrumphing... but especially if she's just opening bouncing ideas off of you for your opinion & or thoughts as an adult she trusts and respects (and who, one is assuming, is getting this party up off the ground).
Son =
1) Ditto... bouncing ideas off of an adult he trusts (being elsewhere, inviting a friend), in trying to figure out his role in this party.
2) Trying not to barge into his sister's party &/or trying to work out what his sister & you want.
3) Speaking quietly denotes being unsure of ones self or one's actions most of the time. Either of the idea, or the reception, or of his 'right' to have a voice in the proceedings (Hey, it's sis's party, why should I be planning it? Isn't that, like, overstepping???). Which, again, is being polite in a natural way. Even if the result is annoying.
The only rudeness I'm hearing, again, is his poking his sister after she has said to stop. Which... HONESTLY... may be the male equivelent of "Love you!". He's saying "I'm outta here" on one hand, while poking her with the other is a sibling sorta "hug". Even when being annoying about it, it's still an "I love you".
________
What do I do? Same thing I do if my son walked up and slapped me (or someone else) in the face. Which is what being rude or impolite is akin to.