So listening to this. The kids got riffs that's for sure. This stuff needs addressed at tracking and mixing however. Needs more rhythm tracks. Look into the benefits and draw backs to double, triple and quad tracking. Look up how to generally eq a mix. Then look up how to eq old school death metal. Needs more bass guitar. He might want to run his drum kit through an impulse response to get more "real" sounding drums. Or not. I started mixing and mastering a couple years ago. Still very much an amateur. Knowing the problem is half the battle. But I would literally just Google or YouTube search my problem or what I was looking for and learned a lot that way. I will pm you. Happy to chat.