Sound is off-time in testing, but I placed them in my timeline correctly.

I found out that the problem is just a glitch with adobe animate, once I exported my animation project into a movie, the audio went fine.

And I forgot to mention that, every time finish previewing my animation through Test Movie, I get an error saying "SWF contains multiple copies of a sound item".

When you test in Animate, are you using Test Movie... from the Actions menu or are you playing the timeline with the control at the bottom of the timeline? The first option should give you accurate playback, the second option, not so much.

if actionscript, set your sound sync property to stream in the properties panel: