Hello, welcome to Rootschat
Firstly, are any of the people you've mentioned still living, if so you need to remove their names as we are not allowed to post about living people.
What does it have on your father's birth certificate? If there is no father then he probably was born before his mother married and really if she wont give him any information I'm afraid there is probably no way of finding his real father. I have the same situation with my brother in law, as his mother wont give him any details. The only thing he can do is keep asking people who might know in the hope that eventually he might get a lead.
Good luck
Jan