How to tell your family

Hi, I’m a 33-year-old mum of three who has just been diagnosed with ovarian cancer. My tumor is rather large, at nearly 30 cm in length, and has unfortunately also spread to my liver. I only found this out two days ago and now somehow have to tell my family. My daughters are 16, nearly 14, and 6.
I have no idea how to start the conversation or how much information to tell them. My treatment plan is still unknown as there will be more scans in the coming days.
I haven’t been able to hide the fact that I’m unwell or in a great amount of pain I was always such a fit and active person running our small farm exercise in our 17 dogs and riding 3 to 4 horses a day however I’ve just not been able to do any of this in the last few weeks as things are growing faster then I would like.
Any idea on how to wrap my own head around this news let alone hep the child understand?