I'm so very sorry to be reading this, Elly.
Before I got to your update, I was just thinking that the best thing you might do for your friend (the surviving partner) is to be there for her and her children even more after his passing than right now.
A friend of mine lost her partner, then just 23 years old, two years ago. Looking at my friend now, this is what occurs to me: Often, the bereaved fall off people's radar after the first courtesy visits and practical help are over with---but particularly when losing someone so young, or indeed when losing a spouse/partner, times can remain hard and coping alone difficult for a few years after. Youth especially can be too busy living or too inexperienced to wait out the grief of a youthful mourner, I find. So just be there... There is immense comfort in just being able to acknowledge the grief, share the loss and relive the good times with people who new that beloved soul that has passed.