I have been all through this (my DH was killed in an accident 15 years ago) albeit, not with children as young as yours.
And I really feel the pain and distress in your post 
My experience is that none of us grieve in the same way and grief is like a spiral. At first the spiral turns very fast. One moment you are fine, the next collapsing under the weight (I still remember sitting on the bus home, 8 weeks after DH died, in floods of tears). As the months and years progress the spiral turns more slowly and you can cope more easily. I still think of DH every day, and a piece of music or sudden sharp memory can bring me on floods of tears, but my grief is gentler now.
You also experience stages of grief, which are well documented. At a year I was angry. Hurt that everyone else was moving on and frustrated that I was being left alone to pick up the pieces.
What I learned along the way, was that these were my emotions and it was OK to let them play out the way they were. The best advice I had in the very early days was to ‘be kind to myself’. If I wanted to cry, cry. If I wanted to talk, talk and if I didn’t want my grief open to dissection by other, then keep it to myself. I also learned to ask for help when I was really struggling.
Your family and friends might be trying to advise you to let yourself grieve, because you are approaching the magic year, when society believes grief should be calming. They may be uncomfortable to see you struggling. The truth is grief doesn’t suddenly calm after a year, it simply softens and becomes more gentle as time progresses and the process takes different periods of time for everyone.
Having gone through the experience, if I was you I would responding to your friends and family in a very calm way, telling them that you need help and support with the children. That you need some time for yourself. Be aware that people often avoid entering your space when you are grieving for fear of saying or doing the wrong thing.
Be empathetic (I am sure you will be) that your in-laws are also grieving, but suggest that they really work on their relationship with your children. 45 minutes is no drive at all for them. Maybe ask your Mum if she could come and stay for a while or have your children for a holiday.
Also look to finding a group like WAY for support from other people going through the same experience as you. That was invaluable to me 15 years ago and I still have many friends from that group.
Whatever you do, don’t be hurt. You are at a really difficult stage in what is a long process and you and the children are the people likely to be feeling the death of your DH most keenly. Other people are unlikely to be being unkind, they are just not experiencing their grief in the same way that you are.