I want to discontinue one of my Apple IDs

See what and how you can transfer from one Apple ID to another here: https://discussions.apple.com/thread/7452747. After transferring, you can deactivate or delete the Apple ID account. Apple recommends doing the first for the obvious difference noted below. But, your circumstances will dictate your choice.

How to deactivate your Apple ID account  https://support.apple.com/en-us/HT208503

“If you request account deactivation, you'll receive a unique alphanumeric access code. When you're ready to reactivate your Apple ID, contact Apple Support, provide your access code, and we’ll help you reactivate your account. If you lose this code, we won't be able to help reactivate your account." 

How to Delete your Apple ID Account https://support.apple.com/en-us/HT208504 

“While your request is being processed, you can contact Apple Support with the unique alphanumeric access code you received, and we’ll help you cancel your request. After your account is deleted, Apple can't cancel the request, reopen your account, or restore your data.”

If you want to share purchases made with the Apple ID you want to stop using, you can try setting up Family Sharing between the IDs if you want to be able to share purchases made with the ID, if you deactivate or delete the ID, you won't be able to do that. I suggest you stop using it, but don't deactivate or delete the ID.

Family Sharing.         

Family Sharing - Set up.