Why is my input from my microphones so low?

I have 4 Behringer microphones (around £20) and a “SOUNDLAB 4 CHANNEL MONO MICROPHONE MIXER WITH EFFECTS“. I am attempting to start a podcast. When I record the audio, unless it is on full blast on all dials, I am unable to be heard. Even on full volume I am very quiet and drowned out by the white noise. The XLR cables I use are the default cables that came with the microphones. As the inputs are all 3.5mm I use a 3.5 to 1.35mm adapter that goes into my input line on my Mac. I record on Garage band. I also don’t have too much money to spend (only around £20-30) and I don’t have a lot of sound engineering expertise.