If I have more than one library, how can I upload all photos to iCloud??

See the quote below from Designate a System Photo Library in Photos - Apple Support

iCloud and the System Photo Library

You can use iCloud Photo Library, iCloud Photo Sharing, and My Photo Stream only with the System Photo Library. If you choose a different library in Photos without designating it as the System Photo Library, the iCloud tab in Photos preferences is disabled:

If you designate a new library as the System Photo Library and then turn on iCloud Photo Library, the photos and videos in the new library will merge with those already in your iCloud Photo Library. If you want to keep the contents of your photo libraries separate, don’t turn on iCloud Photo Library for more than one library in Photos.

I'm not sure but suspect that Photos does not need to be open. You could go to Photos > Preferences > iCloud and see check the status, quit Photos for awhile and go back to the same place and see if the status has changed.

See the quote below from iCloud Photo Library FAQ - Apple Support which doesn't mention a need for it to be open:

When do photos and videos upload to iCloud Photo Library?

When you turn on iCloud Photo Library on your iOS device or Mac, your photos and videos will upload after you connect to the Internet with Wi-Fi and your battery is charged. You can see the status and pause the upload for one day when you follow these steps:

• On your iOS device, tap Settings > iCloud > Photos.
• On your Mac, click Photos > Preferences > iCloud.

Depending on your Internet connection speed, the time it takes for your photos and videos to appear on the Photos app on iCloud and all of your devices might vary. Make sure you turn on iCloud Photo Library on each device.