How Can We Only Have Months Left Together?

Today I am lost for words to describe how I am feeling.
I am not great at talking about how I feel but I have always been able to articulate better through writing. However I am really not sure where to start. So I will probably babble my way through this one!
Yesterday we received the devastating news that we only have months left with Grandad.
Months.......
How do I even begin to comprehend how a life can be measured in months?
For example, the last 18 months, which you could technically measure in years, have flown. I do not want the coming months to fly by. That I think is my fear. I do not want it to go quick as I am not ready to say goodbye. I don't think I'll ever be ready.
How can I make the time we have left count? First I think I need to come to the realisation that the cancer is winning and eventually it is going to win.
I had already promised myself that I would go and see them more often. I had been thinking about going every other week. I wish we could see them everyday but I know I am going to have to settle with every week. I want to see as many good days as I can, I want the children to have happy memories. I know that the twins will be too young to have any memory of their Gramps but Joseph will have.
Joseph......
How do I even start to prepare him for what will happen? As long as Grandad is "well" I won't say anything but when he does start to get ill I know that I will have to say something. I also know that he will be heart broken. How do you begin to tell a 9 year old that his Gramps is poorly and will not be getting better.
If I cannot get my head around it, how will he?
My Nanna and Grandad have always been a huge part of my life and they have always had a big presence in Joseph's life too.
Even though you know its not true, you always imagine them being there and cannot imagine a life without them.
I also worry about my Nanna. How will she cope? I don't think that she will.
How will my Dad cope?
How will my Mum cope?
How will my younger sister cope?
How will I cope? When it happens, I don't know that I will for a while, then again I may surprise myself as we will all have had prior warning.
I do appreciate that we have what ever time left but it does not make it all any easier.
I think that as a family we will all support each other as we are all close and with each others help we will get through this.
We are going to have some hard times coming and I thank God that I have got my hubby and children to keep me strong.