I would assume your front speakers are connected to the HU directly, is it?
Either HU or amp, you can connect in parallel by tapping into it, but make sure your source is stable with the lower load. If your front is 4 ohms and the tweets are 4 ohms too, the source will then see a 2 ohm load if they're connected in parallel.
Ah ok, set pala sya. Basa ko nga yung thread mo sa KAC.
In that case, you will have to remove the stock speakers. Bale replacement na sya. Then tap into that line for the whole set. Follow the wiring diagram that came with it, if there is.