I think the question was worded as beautifully as it could be, Chelsea aren't that good, lol. Semi-finalist 1 = Chelshit / Palmeiras, then which other 3 teams will join the first semifinalist...
But what if I wanted to pick Palmeiras as a semi finalist?

Exactly, you have it already, but aside Palmeiras you still need 3 other teams to make the cut, except you want to pick both Palmeiras and Chelsea and at least that would guarantee you a confirmed semifinalist.
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@Trofo @cryptofrka, this is unique question, like we could have done with a tennis bracket, are allowed to pick two teams from the same bracket, lets say PSG, Bayern ?