Greetings,
While it's technically possible to have a primary channel with multiple sub-channels, it's not customary on YouTube, and it might be challenging for your viewers to navigate between the sub-channels.
Furthermore, each of your four ideas possibly has a distinct target audience, and having them together on one channel might cause mixed messages and reduce engagement. By dividing them into separate channels, you can customize the content catering to each audience's preferences, making it more enjoyable and relevant to them.
However, maintaining multiple channels requires greater effort in terms of creating and maintaining each channel. You'll need to come up with unique content ideas, establish a community, and promote each channel independently. Despite this, if you have the time and resources, it could be advantageous in the long run.
In terms of increasing viewership, having a specific and unambiguous niche for each channel can assist in attracting more viewers. People find it easier to locate your content when they know precisely what to anticipate from your channel.