It sounds as if you have made the decision to stay. I know that when I am very shocked and grieving, I lose the power to make confident decisions, so I am going to suggest some things for you to do and hold on to. This is just to suggest a framework for you to get through the next few days.
When you get home you can start planning the funeral (I did find both of my parents' funerals very cathartic, so this is a date to plan for).
If you are religious, or if you are not and feel the power of churches (they are often very special places because of all the accumulated peace of the years, if this doesn't sound too hippyish) they are great places to sit and think about your mum. Take some time each day to sit and remember happy times with her and your siblings, ideally in a peaceful place like a church.
Go for a walk every day - in the countryside if you can, in a city of you can't. Think of the beauty and atoms swirling around you, and the fact that this infinite cosmos contains you, your mum and your shared love. Bathe yourself in this love. The love is still with you, and always will be.
Set aside half an hour a day to write down your memories of times with your mum, starting with your earliest childhood. Will any of these stories find their way into a eulogy? You can also make lists of things that your mum might like at her funeral, and share these with your siblings by email - remember to be kind to each other.
Finally, take half an hour a day to do something that your mum loved, even if it's something that isn't really you. Why did she enjoy this? Has she transmitted her love of it to you? If not, can you appreciate anything about what she enjoyed? Does it help you to feel closer to her?
Feel free to accept any or none of these suggestions. But I do feel that having some sort of structure for your days for the next few days might be helpful, even if you are out on excursions.
I hope things go smoothly once you are back in the UK, that you will have a lovely celebration of Jean's life, and that her precious memories will forever be in your, and your family's, heart.