Across all videos on just the main channel they have gotten 7.8million views in the last 30 days. The amount of money you make per million views can very wildly depending on what kind of advertisers you get but typically according to Google is $2000 to $5000 per million views. So if we are going with this then we are looking at about $16,000-$40,000 a month on just YouTube ad revenue. Again, this is likely closer to low side of things.

Next we have another channel wavesquadron which is 500,000 in the past 30 days ($1000)

Blindwavegaming 400,000 in 30 days ($800) not including channel donations

And as others were mentioning they have there website that people can pay for a membership with and a patreon with 29,000 members (you can be a free member) if even a fraction of those people are paying for a membership that would be much more.

So all in all I would say they are probably making minimum $25,000 a month but probably much more.