Why did Yosef's brothers refer to themselves as servants of the G-d of his father?
Rashi: They were saying that, even though his father was no longer alive, 1 his G-d was, and they were his servants.
With reference to Pasuk 15.
Why did they say three expressions - Ana, Sa Na, Sa Na?
Hadar Zekenim (15): This is the source that one must request pardon three times (Bava Kama 92a). 1
R. Bechayei: The Torah does not say that Yosef pardoned them. This is why there was retribution later, through Asarah Harugei Malchus. (Had Yosef forgiven them, how could the Gemara derive that one need not request more than three times! - PF)