It depends on the question, cases will be different if they specify a particular quote/paragraph from a speech-and ask you to say discuss its significance and relate it to other speeches, in that case, the specified quote/speech-don't need to constitute its separate paragraphs, but rather you can interweave ideas that can be drawn out from that except into your discussion of the concerns of two other speeches-to be honest-try to make as many links as possible-what speeches works well together often is interrelated by its subject matter-So I think your trio combination is pretty good, I have also given some recommendations in my guide-it is near the end of the guide to save you some reading time-so feel free to check that out when you have time
http://community.boredofstudies.org...-speeches-2015-2020-99-atar-hsc-graduate.html
However, when the speech question includes a specified speech and discuss in relation to say one other speech, the approach you should take is
Idea 1
Paragraph 1: Prescribed
Paragraph 2: another speech
Idea 2:
Paragraph 1: Prescribed
Paragraph 2: another speech-can be the same speech in paragraph 2 or a completely different speech-up to you
Hope it helped a bit