HI and Welcome to Apple Discussions...
log into my websites
From the Safari Menu Bar click Safari/Preferences then select the Autofill tab.
Click the Edit button next to: Other forms
Delete the websites you have problems accessing then click Done.
Relaunch Safari.
If that doesn't help, open Keychain Access (Applications/Utilites)
Select Passwords on the left. Delete the website keychains on the right you have the problems with.
Quit Keychain Access. Navigate to one of the sites in Safari, login with your username and password. You will be prompted to save that data. Click Always Allow. Do that with ther other sites.
If that doesn't work, it may be a corrupted preference file. Go to the Safari Menu Bar, click Safari/Preferences. Make note of all the preferences under each tab. Quit Safari. Now go to ~/Library/Preferences and move this file
com.apple.safari.plist to the Desktop. Relaunch Safari. If you can login to a site without a problem then move that .plist file to the Trash.
Carolyn 🙂