SQL Server AlwaysOn Error:35250
This is login and permission related error. What kind of account are you using to connect when you build the AOA features? If you are using a domain account you can fix this error it in two ways. 


Use the same domain account on all of the participating replicas. If you can't (allowed) change the account you could use the second option 
Add the service accounts that you are using on participating servers into the primary replica. 


N.B. make sure those accounts have at least a connect permission to the instances