Miss - recently diagnosed with a grade 4 brain tumour and I'm struggling with the prospect of leaving my children

Hi my name is Lisa recently 4 weeks ago been diagnosed with grade  4 brain tumor no symptoms no nothing till a seizure 4 weeks ago I have 4 children 27,23,14,and 11 I'm literally in limbo trying to sort sooo much out I've had the surgery then start radiotherapy and chemo Thursday 28th October 2026 I'm not scared of dying but I'm really struggling with leaving my children and trying to get my 27year old to be there legal guardian as there father is useless has them every other Saturday night literally ²⁰ hours every 2weeks this is my wish including my 14 and 11 year old just wondering on any advice or legal help I feel I'm not getting anywhere but it's so close to me heart I'm struggling