@cocopina I'm so sorry to read your post. I have been where you are and it is a horrible and frightening place. All I can say is that you will get through this. I know you probably dont believe it. I never thought I would survive the loss of my mother but here I still am. I can't lie to you it is horrendous but people kept telling me after death it doesnt get better but it gets easier. In some ways it is true that the very very acute sharp pain of grief does recede a little but it is a shit time. I think what happens is that the shock that is necessary to protect your heart eases and turns very very slowly into acceptance. it is always still painful at least for me.
In terms of the position now, you dont say what your mother is dying from but from what you say about her shielding you and that she is planning to go into hospital I am assuming it is something like cancer or a disease that is progressing towards death. If that's right and she is still mentally well, then make sure you discuss with her what she wants to do and why.
most people would prefer to die at home in the comfort of their own bed and home and family around them. has she thought about this or is the plan to go into hospital to protect you/your father? there are pallative care options and support from GP/NHS and various charities to manage end of life at home.
https://www.nhs.uk/conditions/end-of-life-care/where-you-can-have-care/care-at-home/
Separately, but when you haveing a moment where you are feeling as strong as you are able to, I would advise having a google/ read of stuff about palliative care/end of life as it may help you to be prepared. when the end comes, you will want to be there all the time even more than you do now, so its probably worth exploring options for support and care for your child now so you have a plan in place. there are also threads on this forum about this. here are a couple but like I said I wouldn't read them unless you are having a comparatively 'good' day/feeling strong as it is distressing stuff but it will help you to be mentally prepared. I wish I'd known more in advance.
https://www.mumsnet.com/talk/bereavement/4634880-end-of-life-care-and-unresponsive
https://www.mumsnet.com/talk/elderlyparents/4715131-potentially-upsetting-question-about-death
sitting by the bedside of someone who is dying is absolutely exhausting physically and emotionally - because you dont want to leave in case they are alone when they pass. however, it is absolutely essential that you sleep,eat and stay hydrated even if its the minimum. I hadn't realised how long that actual true 'end of life' stage can last after someone becomes unconscious and stops eating and drinking. it can be days or even weeks. It is apparently very common for people do die when relatives who have been by the bed for virtually 24 hours a day nip out to go to the loo - sometimes I've heard it said that its thought that people do this by choice to spare their relatives and want to die alone, of course it could be coincidence or a lack of stimulation in terms of touch, voices and so on - so if this happens dont beat yourself up and be aware that it is possible.