When I simultaneously record more voices I have troubles equalizing the tracks.

Sound leaking in the undesired microphones is a big source of distortion, this it is due to summation of the direct sound with a copy that is very close in time (a few milliseconds), so close it cannot be edited. This phenomenon is the reason professional music albums are recorded with separate takes.
It is not so uncommon to have this problem, think about a radiophonic program with two or more speakers or the case of a rock group wanting a fast and economic demo record of their music.
I will answer with some quick simple concepts, looking the matter from the usual point of view of Acoustic Physics.

First thing is to exploit the microphones directionality and their disposition within the room to minimize these leaks (the commonly used cardioid or hypercardioid microphones are the most sensitive right in front of their membrane). Using mobile partitions can help, although the sound attenuation they give is never astonishing it can be good enough for not so loud sources. If the room is large enough distance can help too, remember that sound pressure level drops by 6 dB every time we double the distance from the source.

In the case of quickly recording an electrified band a good tip I learnt from an old engineer is to turn the guitar amps towards a wall that is treated with sound absorbing material.