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They're all correct, as long as you don't try to use them both at once :)

"don't take the trouble" is okay, "don't take that trouble" is also okay. "don't take that/the trouble" is definitely not okay - I think you know that but just to be sure! "the trouble" will usually be more natural.

"this reaction" and "that reaction" are both okay, but "that reaction" is probably more natural. "this reaction" would maybe be if it was something close to you - you send someone a letter and you get a reply, and you're holding the reply in your hand, you read it and tell someone "I didn't expect this reaction". Because it's close to you, in your hand. But it's a very fuzzy distinction, both are okay.

"it's ok" "that's ok" both fine. "it's ok" would maybe be preferred over "that's ok" if it's something that's close to you. "I'm alright. I walked into a door and got a big bruise, but it's ok" - probably not "that's ok" in that sentence. In your sentence, I think they are both equally correct.