What can I do to help?

I find myself asking this question a lot lately. After my sister and brother in-law had their baby I've asked them how I can help at least twice a week and every time they tell me "nothing but thanks for the offer". My sister in-law I swear is just too sweet to say something. 

A couple of days ago my dad had surgery. This is scary because I have a fear of losing him. When he's gone I have no parents and no grandparents. Yes, I have the in-law side but we all know it's not the same.  Anyways after the surgery he came home and he hasn't been able to do much and his wife is sick and can barely talk. So I ask them daily, what can I do to help? And again I get the same response "nothing, but thanks for the offer". 

Is everyone this polite and strong willed that they don't need help anymore? I hear about everyone’s struggles and I offer to help but it's not needed. Maybe the only way I can help is to listen. I try to be a good listener, but for example listening to my most caring little sister, Alecia I find myself in the middle of the conversation interrupting her to talk about myself. I love what she has to say and I want to know everything about her life (well almost everything). So why do I do this, bad habit I guess. I find myself doing this to a lot of people, I'm I really that self absorbed? I don't know, Sometimes I wish I could just be someone else for a day and observe myself and see what I'm really like and what I need to work on. I'm sure the first thing I would say is "Dang, I'm fat!" My poor husband I just seem to dose off into space somtimes in the middle of our conversations. 

But I really do want to be a good listener and be less selfish. People are so sweet and keep giving to me and I just feel I have nothing to offer them in return. So, what can I do to help?