Oh my love - I am so very sorry to hear this :( In my experience the only way to cope with shock & bereavement is one minute at a time, don't think too far ahead.
You will cope because you are a Mum and both of your sons need you. You will cope because you have to :(
It would be incredibly generous of you to allow James' friends to make a contribution to his funeral - allow them to suggest songs/readings/things he might like (as QuickLookBusy suggested, a book to write them in might be the best way) and if you can bear to, open your home to them - you and they will get a lot out of that.
If anyone offers practical help, ask them to make small things that you can nibble on, bite size sandwiches are perfect. You probably wont want to eat, but you need to - tiny bits you can just eat without thinking will help. Also, keep drinking water/tea/juice. You need to keep your strength up, your body is already with a massive shock & will cope a little better with food/liquid.
I am sure James knew how much you loved him, it is clear to see. Please, please remember it was the illness that killed James, in the same way that cancer, heart attacks & other illnesses kill people. Hold onto that.
I will be thinking of you and sending you love & strength x