Can people please share their opinions? I managed to intercept several domains that were not paid for and found out they have traffic. I conducted an experiment by exposing the old owners through the ns server, and their sites started working again. It now appears that my domain is linked to their website. How can I put my banner on their site?
 Should I use a frame with a banner to transfer the domain or download their site completely, place banners, and upload them to my hosting?

There is no guarantee that the hosting will be renewed as the domains have been abandoned. Consequently, when the payment for hosting expires, the websites will stop functioning.

 It is recommended that you contact the previous owners to determine why they chose not to renew the domains, whether intentionally or accidentally. If they happen to be interested in repurchasing them, you could sell them back at a similar price.

Try to download the site entirely. Either with the current dns, or from the web archive. And host it on your domain.
Then you can put any advertisement.