How do you paragraph dialogue when multiple characters are acting?

Question

So if I'm correct, you start a new paragraph in dialogue every time a new character is the one focused on. So if character A says something and then does an action that's all one paragraph, but if character A says something and then character B does an action you'd need to separate those things with a paragraph break. But what if character A does something and then both characters are involved in the non-dialogue text? This is the sample at hand in case anyone's confused: *"Time sure flies when you're having fun…" David frowned and for a moment Morgan detected something strange in his expression. "You should be nicer when you talk about your father, he's a good man: he looks after you and it's pretty clear he loves you very much."* (both pieces of dialogue are being said by the character David)

Answer 1

Interesting question! Yes, you would start a new paragraph when David resumes speaking.

As you know, in the U.S., we further denote direct quotes by opening (and then closing) quotation marks, while in Britain, they use the simpler technique of setting off the new quote just with a dash.

--Dr. Robert A.

Answer 2

You would write that exactly as is, with no new paragraph when Character B is added. Leaving the dialogue along with the actions will indicate to readers that Character A is still the one speaking.