Mom's health is seriously deteriorating. How and when can we help parents move in with us?

My hubby is in the military so we don't live close. My mom has had back issues for years but over the past 5 years her diabetes, ciliac, and autoimmune problems have gotten worse. She has also gotten bad nerve damage and looses control of her legs and gets awful cramps. She's needed a cane and has chronic pain for a few years now. My hubby is in the military and so we don't live in the same town. We live close enough that we can drive over and visit a few times a year but not close enough to help as much as it seems she needs. She recently hurt her knee(not following doctor's orders) and is on bed rest for a week until she can get into the surgeon. Everytime we visit we are more and more concerned for her health. My dad is there to help her when he's not working but it is obvious that it won't be long before she will be in a wheelchair and worse off. We feel like its just a matter of time before she needs in home care during the day. I can visit for a couple weeks to help her recover from surgery but soon that won't be enough. We've tried discussing the possibility of them living with us in a mother's den apartment that we could add to our house. Whenever it is brought up they refuse to admit that they might need it and won't let us discuss it. I understand wanting to be independent but we are worried and want to help them. When the doctor tells them that mom needs in home care we want them to already have the peace of mind that they have a place to go. With my husband's military status my mother at least could be listed as a dependent and receive better insurance and ensure that we can take them with us wherever we get stationed next. Has anyone had similar circumstances? Any advice?