Use AD for internal authentication and ADFS for external on Sharepoint environment

I've have this environment: WAP (WorkGroup) + ADFS + SharePoint. I have this doubts

1) is it posible use Windows Authentication on internal users and ADFS on external users ?

2) When I configure WAP to use ADFS preauthentication, it doesn't work for external users. Pass-thought preauthentication works well...

Regards