What are the proper punctuations required in the stylistic phrasing: "from [location] to [location]; from [else] to [where]"?

Without more context it's hard to tell what this sentence is trying to do. As mentioned, 'tasks' is probably not the right word for something like seeing friends.

In my mind the colon says you are about to talk about your tasks you were accomplishing (the direct object), but then in your list you lead with the places you were travelling to/from instead. So there's a misalignment of focus that is making the sentence sound off.

Some ideas:

• "I was abroad to accomplish these tasks: Meet up with* my brother (Denver to Paris), and see my friends (from Milan to Seoul)."

• "I was accomplishing tasks while abroad: In Paris (leaving from Denver) I met with* my brother, and in Seoul (leaving from Milan) I saw friends."

*insert your own verb

On its own I don't think punctuation is going to perfect this sentence.