OK, at this point you're getting a lot of suggestions that are just going to take further down a rabbit hole you need to avoid. If you're going to mess with different router options in such random ways you're going to end up with a home network that's not stable, not reliable, and not secure (stress the point about 'not secure').
If you're tried three different extenders, it's probably not a problem with all three extenders (odds are very, very unlikely). Sounds more like a matter of just setting up the extender to work with your existing router.
Given you're not familiar with basic networking, instead of trying to educate yourself by experimentation and trail-and-error guesses, it might be more prudent to just hire a local contractor to come to your home, set up your home LAN properly and securely, and ensure your entire household is getting adequate WiFi coverage -- which might involve using an extender or extenders, or just getting a good router, or going to mesh system, or one of numerous other options. Be sure to stay involved in that decision-making process, observe what's being done, and document the final set up so you have solid, working info in the event you need to alter things on your own later. And don't look at this as an expense but rather an investment in yourself. There's no need to aggravate yourself with having to always fight with an ailing home network and intentionally putting your own privacy and security at risk.