Your eldest child would probably be OK to go, and it will probably help him come to terms with losing grandma. Saying goodbye is distressing but its a part of the grieving process. My grandma died when I was 8 and I wasn't allowed to go to her funeral. I had to go to school as normal though I knew what day it was. Although I knew what death was and understood that she'd died, it took me years to come to terms with it and I honestly believe that it was because I didn't get to say goodbye in the same way that everyone else did.
If you want to pay your own respects, could you perhaps go later than the rest of the family and sit discreetly towards the back, then leave straight away? Obviously this would be difficult if your ds does go, though.