alt Hacker NewsI don’t want to take away from OPs project (which seems really nice) but have you tried Ultrastar Deluxe ( https://usdx.eu/ ) in combination with USDB ( https://usdb.animux.de/ )?
There’s also a program for automatically downloading the songs: https://github.com/bohning/usdb_syncer
Someone also shared https://github.com/rakuri255/UltraSinger
Which seems to output something that works with Ultrastar.
My sister loves karaoke as well and we grew up playing karaoke revolution and rock band. Shame they don't really make those anymore.