multiple website in same domain with same content

I’d probably start by using categories to distinguish between the three. You can add category-specific menu options for now and expand on that into subdomains if the need arises.

You can share databases between multiple sites by using different prefixes but sometimes that grows pretty big and you might need to move the data tables for the individual sites to discrete databases later.

You might explore going to a multisite after a time if you decide to start with using the categories. I’ve done that and then moved to discrete sites before. It’s a natural progression.

You’ll need to synchronize content between sites if you wish to have the main site and then run discrete or multisites with the main site directing users to see more content on the subsites. The prefix distinguishes between the sites.

Finally, you can often run one database for more than one website even when the other sites are hosted elsewhere. Your database host needs to know to provide database access to outside hosts.

I’d suggest getting started and moving up later as needed.