I wanted to know if my messages will still be visible to the people I sent them to in the past when I delete my whatsapp account. I basically want my whatsapp messages to be deleted from their phone.
No they wont be deleted and stored in a private whatsapp directory. When you again Install whatsapp it will search for that content and if found you can reload all your contents with news version installed. And you do not have whatsoever any control on the messaged that you have already sent to other users they are stored locally on their side So just deleting your account does not make them vanish from other users device.
The messages will remain on the WhatsApp interface.
Also, there is a history of all conversations in the WhatsApp folder on your internal storage. You may also want to get rid of them, if you don't want backups of all of your messages.
Basically, once you send a message to someone they receive it and it goes to their storage, so you cannot delete those.