I've been thinking about your post since I read it this morning. I can't really top what I just quoted from Marc (beautiful)... but i feel compelled to add a bit more to my earlier response. Typically I don't delve too deep into my personal life online but what the hell.
My mom is in the midst of her third battle with stage four fully metastasized ovarian cancer. We have NOT been given the diagnosis of "terminal" and we have definately not been given any sort of deadline. We are approaching this with as little fear as possible because in this instance fear serves no purpose. In that major way my situation is quite different from yours.
Something that we do have in common though is that realization of how important someone is to us BEFORE they are gone. We both have the opportunity to take some control of how our relationships conclude. Being able to spend time with the person and express to them exactly what the mean to us is really a gift. I have lost a close loved one unexpectedly before and there are things I really wish I could have said/done that I didn't have the chance to.
You are going to be able to be there for your dad and your brothers in a way that will be complete and can be without regrets. In light of what you wrote above i would suggest taking some time to really think about what you want to say to your dad. If I were you I would do some writing on it also. Write a few letters to him... you can use them as a basis for your conversation with him or even read them to him in person. I know they will mean alot.
Your dad might not express things to you in the way that you hope... sometimes it is hard for men especially older men to vocalize their feelings... but you will be able to say your part and that is most important. Also think about what you dad might want you to do for your brothers. Even if he does not initiate that topic (he may not want to burden you) take the opportunity to tell him what your plans are in regards to your relationship with them. Even though you don't live in the same country letting him know that you will be there for them will probalby ease some of his fears in that area.
One thing I have been sure to do for myself is to talk about my situation with my close support group. Be sure you have one or two people that are there for YOU as well as you being there for your family.
Again, I'm really sorry to hear this sad news.