I think its an absolutely admirable thought that you have @Blackjack . I do not have a physical condition but have the same concerns regarding their feelings of the children left behind which are similar of ages. Death is a selfish event and i don't mean for you. When someone we care for dies its how that individual copes when someone passes. Each individual will deal with it both within their own head and as a shared consciousness with peers, in this example, the two brothers that are your sons and your husband who is their father. Sometimes the smaller the family, the better the connection and support for each other. Sometimes you can be surprised at how people, whether it be a close family situation or a work thing, that when a key person goes, they adapt and change and make it work. Your 17 year old is possibly (but I don't know) a bit more mature than you think. As parents we still have fond memories of them being babies and forget (or ignore) that they are moving on and growing up, but still have that overprotecting behaviour towards them. I know my sadness comes from never to be able to walk my daughter down the aisle at her wedding, go to my boys bachelor parties and embarrass them, see grandchildren and all of that good wholesome Disney stuff. But that's my sadness, not theirs. They may share the same dreams and desires for you to be around to see that and for them, those events may always be tinged with that sadness.
My ex-wife was ill for a while shortly after the birth of my 3rd child and had to be hospitalised, on paper I was a bit of a typical male, not doing that much in the home, she had her female relatives and friends come round to check on me at least twice a day. It took me a short while to acclimatise, but I did. The friends stopped coming round purely for the quality control check and more just came to see the kids and give me a 10 minute break, the kids ages ranged from being a baby to a 6 year old so it was many years ago. In short I am trying to say that as humans we can be adaptable, they will find their path just as they have done with coping with your condition. There will probably be a time, whether it be in the near future or many moons ahead that they see the reason for what you did and appreciate that life with suffering is not really life. That you took control from the uncontrollable and you left on your own terms with your dignity and strength, even though you wish you never had to.
You sound like a fantastic mother and you have said that they have a great father. The way you have raised them if my guess is right would have given them individual strength, you have provided them a close bond so you have given them family strength and the memory of a mother who did what she believed was right in the face of adversity with all the facts to back it up. I would personally be proud to have a mother like you.
As a personal note, my mother died with dementia. Didn't know who I was and when I visited, she thought I worked in the care home rather than the son that I was. I would personally prefer to have remembered her before that vile disease took her from me way before her body left, she was quite the firecracker. For me she died three years before her actual death and that was quite hard. I know its a completely different medical condition but just from a son's point of view I thought I would share.