Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
It is not weirdly connected. Let me explain why it is that way. Each application you downloaded using a particular Apple ID is tied to that ID/email address. That means whenever you try to update those apps from App Store, it will still ask for the original Apple ID/email used to download it regardless of what ID you signed on your iPhone now. Sounds like those apps are originally downloaded using your ID, thus it is asking for your ID. So what you want to do is, just delete those application and redownload them using his ID/email and then that application will be tied to that account.
Deleting the app will also delete its contents. It won't delete anything of server based apps like Facebook, Emails etc.
To delete, just tap and hold down the app and it will start wiggling. Tap the x icon on the app and it will be deleted. Then open App Store, search the application and download it using his account.
Important : On his iPhone, go to Settings (select your name) iTunes & App Store and make sure his ID is signed there. If you see old your Apple ID there, then tap it and tap Sign Out. Then sign in to his ID
If you have any questions or would like any additional information, please don't hesitate to ask.
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