I know, not what you want to hear, but it's likely these sites that you're visiting simply do not support the Windows 7 version of your browsers anymore. If you really want to know, download Oracle's VM VirtuaBox and create a Windows 10 virtual machine. Install the latest browser that isn't working on Win 7 onto your Win 10 VM and visit the site. If it works, then you know.
If you must stay with Windows 7 then make sure Windows Updates are at least enabled, the root CA would normally come through that. If this doesn't fix the issue you would need to find out which root CA each website is using and manually update the certificates.