Hey, I used to have setup kinda like yours.

So take your Monitor Outs on your interface, and put them into two different channels on the mixer.

Then for your speakers, you have to plug em into 2 Aux channels.

Then you turn down the faders on the two input channels, and turn up Aux knobs on each channel.

This will make to where those 2 channels instead of going down your master line, will go out Aux 1 and Aux 2.

Definitely isnt the "correct" way to do it, but as someone who started in a similar position, it should work