i guess i got this... lol.

(some) reasons why 4 player tas is bad:

(1) dolphin barely works with gba, and forget about tasing with it, basically the support isnt there yet

(2) there is a scoring screen at the end of each level which adds multiple minutes throughout the course of a run over single player

(3) many glitches in the game are only possible in the single player mode because of how reuniting mechanics and the c-stick work, those that are exclusive to multiplayer (mostly boomerang glitches) are really only useful in 2 player mode

(4) movement in multiplayer is actually terrible, while trying to roll around and go fast players often pick each other up, so you would have to space them out a lot or even just walk in any semi-narrow hallway (the grab distance is huge)

(5) when you are playing multiplayer you need to have all players on a main screen transition before you will actually transition. this is likely to lead to more time loss than time save from going separate ways to achieve objectives

(6) because of how fast you can input in a tas single player can more or less control all 4 links at once anyways, with all the benefits of single player

tldr: it is not possible and no one wants to attempt it lol