Can I use these songs in a game engine that's not GBstudio, like Unity for example? Also can players/creators monetize videos or livestreams containing this music without copyright claims, DMCA takedowns or demonetization?
Viewing post in 8-Bit Gameboy Songs DX - THE COMPLETE COLLECTION comments
Both of those situations are allowed! These sounds are usable for commercial and non-commercial products, which includes games made in any engine, as well as things like videos, live streams, and monetized content
In each case, the main stipulations are that credit is to be given to "TipTopTomCat", and the assets cannot be redistributed or claimed as your own work as noted at the bottom of the project page