What form do i get my wife and daughters to sign to allow me access to their online CRA accounts?

If you just want to use Auto-fill in TurboTax, then you just need their permission and their login details. 

If you want to sign up as their representatives with the CRA, this page has more information on the process: https://www.canada.ca/en/revenue-agency/services/e-services/represent-a-client/about-represent-a-client.html