but I can't imagine how my father feels
This always puzzles me. Usually we say something like this to be supportive, but how supportive is it to tell someone that you have no clue what they are going through? To me, it seems like removing the ladder while someone is on the roof. But at the same time, if we do claim to know how it feels, they might challenge us.
So I suppose it comes down to specifically how much of an epistemic limit the subjectivity of feelings is. On the one hand, I'd like to say that we can imagine to some degree what it might feel like, but on the other hand I am loathe to accept that claim that transsexuals "feel like a woman inside", etc.
My usual retort to that is that one only knows what being oneself feels like, and that there is no good basis whereby to seperate what it feels like to be a man or woman from what it feels like to be black or white, etc. Our feelings are only differentiated over time, but being a man or woman, or being black or white, does not change over time. Certainly we might make some claim about what it feels like to be young versus what it feels like to be old, because that changes over time.
Along these lines, I'd like to say that if one has experienced grief, one can rightly claim that one knows what grief is like. Grief does alter over time. Therefore, I believe you should rightly be able to claim that you can imagine what it feels like, since you (presumably) have experienced grief to some degree.
Even if the grief of losing two parents is of a greater degree, any experience of grief should compare.