Ok I see, that’s a messy solution indeed.
Ideally you want the mixer as the central hub where all signals originate or go to. I don’t know the soundcraft mixer too well, but I’m sure there’s a way to connect your instruments to your mixer, your speakers to your mixer, your computer input to the mixer and the computer output to the mixer.
Additionally, I could be wrong but the way your speakers are connected now you aren’t getting a stereo image. These are stereo inputs on mono speakers so they are summed together and both speakers produce the same mono signal in this case. Get rid of the RCA inputs on your speakers and just use the jack input on them, left output on the mixer to the left speaker and right output to the right speaker.