How do you do it?

Wow, I don't even know where to begin.Ok I'm a 29 year old only child. My husband has been in the Air Force for 16+ years. We haven't lived near my parents in about 10 years. My mom is 53 and battled breast cancer 3 years ago. I left my husband alone for 6 months to help her through her battle. My boys were 4 and 1 at the time. She lost both breasts, did the chemo and radaition thing and is doing AWESOME! Last May my parents sold their home to move near us. The same week they sold their home, we found out that my dad had lung cancer. After getting here, he had surgery and found that it was inoperable. He did the chemo and radation thing and for a man of 73 (yes, they are 20 years apart) he did awesome. Within the past 6 weeks however, he has taken a dramatic turn for the worse. It is not the cancer...it seems like Alzheimers. He had eye surgery today for cataracts. I'm hoping that him seeing again will help. He is unable to perform most of the basic tasks that have never been difficult for him before like using the phone or microwave and remembering appointments times/dates. We have an appointment with his family doctor tomorrow. I guess I'm just looking for a little support. My husband has been gone for 9 months and is due back in a month and a half. I feel very alone in all of this and am worried sick about how I will do this again in 20 years with my mom. I'm also dreading summer vacation starting as I will have to find care for both of my kids for all of my dad's appointments...I've been able to sit with him a lot so I don't worry so muh but I can't do that with 8 & 4 year old boys over the entire summer. 

Thanks for reading all of this and for any advice,