It's a tricky thing for sure. In this case with TikTok, the username of the creators are always shown in the video. This is shown by default by TikTok. You have the right to share this content with anybody, as long the creators are credited. If a creator copyrights their TikTok content (which can be done through a YouTube creator network), they can put a claim on your video. When this happens, they will get a part of the earned revenue.