Is it authorized to use "remix" and "audio samples" samples bitpack from BotB in non-BotB tracks ?

yes and no. bitpacks are often not original content which already likely makes it legally dubious, no matter what any botbr has to say, but also: literally noone is gonna chase you for using samples ripped from games and the like (especially when they're one shots and it's *impossible* to unambiguously determine the origin)

shit I don't even know what the license for bitpacks is

there's nothing on BotB stopping you from using bitpack content, which I assume is the primary question here. but as wormie indicates, this has no relevance to the rules of law or whatever, that's a separate bag of worms

I guess "sample" battle submissions are under the same CC license as other entries

and thus fall under the same "non-commercial use" banner - so don't use sample entries in works you're charging money for, and be sure to clearly attribute them