Sending you a warm welcome that must be so difficult for you and being so far away won't be helping.I think on those times you do get to see him try and create somevhappy memory's for you and the children and try and take one day at a time rathervthan anticipating what is to happen.
Also try not to worry too much about being strong for the children youngsters can be remarkably resilient and also if they see you upset its a message too them that its OK to feel sad and its OK to cry. But as well as making any happy memories with him now it might help to also think of ways you may be able to help them associate him with happy things into the future and a way to feel close too him that is also a positive thing for them to take into the future.
.Maybe think about what you will tell them when the time comes so you and your husband are in agreement and saying the same thing. People send balloons up or plant memory trees,doing something like that will help you too. A friend recently lost her husband and they told the 3 year old grandson Grandad had gone to the moon,so every night at bed time he waves to the moon.The thing with that is they can wave to the moon from anywhere in the world.
My grandkids send things down the river for their grandad,flowers feathers paper boats,its part of picnicking there so a fun occasion but I know the eldest who was close too him goes there now on his own just to feel close too him still, as do I.
It really difficult to say that because none of us wants to think of what is to come,but you're thinking about it anyway,doing it this way maybe will help.Nothing will take away the pain but just maybe,having some kind of strategy to call on when the time comes can take away some of your worry over the children.
Also stay with us we will be here for as long as you need us.All of us are on this grief journey so do understand.