Aw im so sorry to hear that. Could you not maybe treat him as though he is one of your close friends [even though he is]. I should imagine you know him really well so just do what you feel is best. When you loose someone close to you its always nice to know that someone is there and that they care etc.. So dont worry about feeling like youre annoying him. But at the same time you have to understand that hes upset and that he isnt going to be his normal self for sometime. I hope hes okay and good luck
RIP to his dad.