All the patches are cumulative in nature which implies that 6.3.3 has all the previous 6.3 fixes. You need to install 0028 JEE patch and run the configuration Manager. Once completed the adminUI 'about' section should show this new patch version. It confirms your successful update to 6.3.3.
Yes, 6.3.3 is the latest patch that you can apply to your instance. You need to raise a support ticket and support would share the ftp details for the JEE patch download. On the other hand, OSGI side patches are available on package manager and you can get the direct download link from below document: