Keep in mind that when you're viewing your photos using the Google Photos app, it's just displaying your photos in a graphical, arranged way. So when you create an album, the photos in that album are just being shown to you that way. The actual photo files themselves are a completely different manner. The Google Photos app is for viewing and such, but you need to dig down deeper and use an actual file manager app to manually arrange, sort, and re-organize your photo library. Depending on how big your entire photo library is, this is going to be something of a daunting project. But once you get all your photos sorted out it's a lot easier in the long run to maintain everything in an organized way.
There a lot of good file manager apps out there. They all have the same basic functionality with the big differences being the user interface, and a lot of them include more features like added networking capability so you can manage files/folders both in your phone, connected devices, and online storage services. So it's important to pick the right one that suits you particular needs. We all have our own preferences so what I might find to be best option works for me but might not for you. Go the Play Store, do a search for file manager apps and find the one that you like. Read through the feature listings of different choices, find what you want, and look through the screen captures for which ones that have a look and feel you'll be comfortable using. I'll suggest 'MiXplorer Silver' app -- it has a really extensive feature set, but a very popular file manager that gets a lot of good press is 'Solid Explorer' app. But again, pick what you find to be what you like. You might just want a simple, basic file manager. If you have a Samsung phone, it already has in included file manager, the 'My Files' app.
Anyway, once you have a file manager utility then it becomes a matter of getting control of all your photos. That can be a real chore as there isn't an established default any longer. At one time there was a DCIM folder (Digital Camera IMages) that was the more or less central location to store photos. But now it's something of a mess as depending your phone model, the version of Android its currently running, and which apps you have installed on it there could be a DCIM folder or using names like Photos, or Pics, or Images, etc., with the added twist that browser apps and text messaging apps usually default to a Downloads folder, and some apps might use their own folders. So it's likely you have photos scattered in different locations in your phone's storage media. And since you want to exclude some of those WhatsApp images you need to be more selective about which files you move around. Again, this could be an involved task.
But it's important to differentiate between how things get displayed to you (using the Google Photos app) and actually maintaining your photo library (use a file manager app to actually manage your photo files themselves and their folders). Also, if you start nesting folders within other folders than you will need to go into the Settings menu of the Google Photos app and add those nested folders so the app will auto-index and display your content.
