Make sure the Source code is not disabled when downloading.

Then as you can see on the picture, selecting "Source Code" will tell you exactly where it is located.

Notice that I've downloaded the 32 bits version to make sure to reproduce the same use case as you.

Edit

As per your new edits and comments, it seems what you want to know now is why you don't see the installation wizards. I'm pretty sure this is due to old-set registry key.

Run the following command

reg query hklm\software\microsoft\windows\currentversion\installer\UserData\S-1-5-18\Products /f "java" /s | find "HKEY_LOCAL_MACHINE"

Now, navigate to each of the returned path browsing with regedit and delete their entire parent (the big hexa number).

Re-try the installation and I'm pretty sure you will see the wizard.

As for the sources, Oracle documentation specify how to download them in silent mode.

jdk.exe /s ADDLOCAL="SourceFeature"

Java JDK 8 is available at :

• direct link
  
• Oracle Website

To ensure jdk is installed, just go througt the following :

1. press Win + R

2. type 'cmd' in the popup and press button OK.

3. in the console which has oppened, type javac -version and press enter.

You should see as an output :

javac 1.8.0_XX

If so sdk is installed.