If something as small as this makes you feel upset, you must live a charmed life. These sort of problems, and much worse occur in most families. What most families do is swallow hard and find a fix. As others have suggested a Christmas Eve visit, or even make a big day of New Years day.
Anyway children the age of your DGC are inundated with toys. On Christmas day your presnets to your DGC will just be caught up in a jumble of other toys, make a big day of the New Year with the children getting your toys, after the novelty of all the new toys has worn off and they will really enjoy having more toys and with nothing to distract them will appreciate them more.
When my children were young we never spent Christmas day with my parents. They had my sisters with them and sometimes an aunt and DH, so there was nowhere for us to sleep. DH;s parents always stayed with us. He was an only child and they did not drive. But every year we all got together on Boxing day, at one house or the other and my parents had all the pleasure of seeing the children unwrap the presents they had chosen.
We only see our grandchildren on Christmas day every other year. Otherwise we do not see them until the 27th or 28th.
Why are you so unkind and carping about your sil's parents disabilities. If someone has carers, they will need them, the Council will nto pay unless the hneed for caraers is high and those paying for themselves, unless millionaires, need to consider the cost, which is not cheap.
And as for booking somewhere to eat. It can be done on a phone. Phones can be operated quite successfully while chair, or even bed bound.