I got to page 7 and couldn't stomach reading anymore because there are some really unfortunate and unsympathetic posts on here.
I've cooked every Christmas Dinner mostly on my own, hosting family and/or friends from when my children were babies up until my hubby and our now grown up children started helping out more and even taking it in turns who is doing the big event. I also do remember exactly how difficult it can be with small children and visitors. It is a juggling act and can be extremely stressful.
I also lost my own mum 5 years ago, and I also do voluntary counselling with a bereavement charity.
No matter how well your husband has shown you he's coping with losing his mother, he is still grieving for her and 'not over it'. People don't just magically go back to normal within a few weeks or months. Even 6 - 12 months on (or longer) his emotions can be swinging back and forth like a pendulum from the extreme of feeling totally devastated through to the middle ground of numbly functioning with day to day family life because he has to, and the more positive extreme of finding meaning or joy in life again, which can make him feel guilty about being happy when she's dead and plunge him back into his bereavement again.
Whether you or he realise it he will be moving between these two extremes constantly. This is quite normal. The frequency he swings between them is nothing to do with how long its been since she died, its all to do how far along in the grieving process he is. That's different for each person.
Certain times of the year Christmas, New Year, Mother's Day, Easter, her birthday, anniversary of her death, anniversary of the funeral and whatever other dates have meaning for him are going to be really painful and will be for a number of years. This is also completely normal. And the worst ones are often the Firsts. The First Christmas, the First Birthday etc.
So this Christmas he will be emotionally all over the place, and despite the happiness of a family Christmas with you and your children, even with the distraction of having your family there - everything will highlight that his mum is no longer around. Things have moved on around him but he's trapped in his loss.
Its not wrong to have your family there this year, its just different, and its facing and accepting that things are now different with this mum gone that he is in the process of doing - but its going to take time. There is no right or wrong way to grieve or for him to act or react. He's never lost his mum before. Its a first for him. He's trying to cope with something he's never experienced before for the first time and its hard.
In the same way you are changing things by having your family round, he needs to change things as well within himself as a way to work towards accepting his loss. I suspect he's going to the pub to meet with friends where he can just be himself and feel his grief without spoiling Christmas for you, the children and your family. This is giving himself important time to mark the occasion and give him a chance to think of her before returning to the whir of busy family celebration. He's not trying to shut out his loss, he's facing it, and its quite healthy and brave to do that.
Everyone grieves differently. There is no right or wrong way. But he needs your help to get through this Christmas and if that means taking an hour out to raise a glass in private to his mum with the support of friends I'd facilitate that if its what he needs. Surely your family can help you with dinner and with the children. By supporting you, they are supporting him. Why doesn't your dad go with him.
Yes that divides the 'boys' and the 'girls' and people here have already cried out in protest of inconsiderate sexism. But unless that's what your husband is like every day, I'd say its not sexist stereotyping but grief. Grief isn't sexist or discriminatory it equally hurts people of each gender.
You could possibly consider maybe doing something for your husband in a quiet time on the day when its not as busy to show you are also respecting his loss. Maybe planting a Christmas Rose in the garden in her memory - Hellebores are perennials and come back and flower at this time of the year, year on year.
And OP, I do understand the pressure, but then take that pressure off yourself and stop trying to do everything perfectly this year. An important member of the family has died and things are allowed to accommodate that. Plus when you have small children you need to cut yourself some slack and allow that little ones have a way of making the best laid plans go kaput.
Factor in SCRF - Small Child Random Factor so if it doesn't go to perfect timing then so be it - its not the end of the world. Your family will understand. You will have plenty of future family Christmases where you get it all to run smoothly (so speaks the paranoid planning control freak here), but your husband only has 1 First Christmas without his mum.