Unauthorized access to my iPhone messages and conversations

If it's happening with two phones, then highly unlikely that someone has compromised your phone. That is difficult to accomplish even once and would require highly sophisticated (and expensive) tools and in most cases physical access to the phone. I can't say it's impossible, but again, it's very unlikely.

I know you say that you have changed passwords to your Apple Account, but there are some additional suggestions here that may help:

If you think your Apple Account has been compromised - Apple Support

And of course you need to make sure you have secured any other online accounts such as with Google and your cellphone account (many service providers have websites where someone with access can see call histories, messages, etc). You may need to talk to your cell provider about this.

If you continue to believe that your phone or accounts have been compromised, you probably will need to contact a security expert for further assistance as it will be beyond what anyone of us in a public forum can do much more to help with.

Regards.

Eves dropping on phone conversations is a violation of federal laws. Contact your local police department and then contact the FBI. They have the tools and resources to assist with your issue.

No one here will be able to assist. We’re all Apple users like yourself. Apple Support is not here and will only assist law enforcement.

Your phone was not "hacked".

Your Apple account may have been.

If you think your Apple Account has been compromised - Apple Support