Is it permitted to cite works by members of my own family?

I'm starting a unit at my university which deals very much with topics researched by my grandfather - He has written a number of books and papers on the issue.

I don't yet know if I'll need to cite them but I thought it would be . Is there anything I should take into consideration if I end up citing his works?

Additionally, would it be considered unethical (and/or an 'unfair advantage') to clarify anything on the subject matter with him, or does that just constitute "good research"? If I did get clarification from him, would I have to add my communications with him in an appendix?