Hi, welcome to this community although like everyone else here, you would rather not be in it.
The thing about grief is, nobody knows how to cope with it. You just struggle through, doing the best you can. A terminal diagnosis is particularly hard. In medical terms, this means I think that whoever it is is expected to die within 6 months.
Your mother’s prognosis of a month to live is based on her doctor’s expectation given her/his knowledge of disease progression. I hope you have a good palliative care plan in place - this should give you access to a number that works 24/7 to answer any question you may have. The district nurses should be visiting daily. And carers should be provided to help.
This is called NHS continuing care, which is automatically available to anyone with a terminal diagnosis. I hope this is in place, if not you need to call you GPs to put it in place.
A someone who’s 6.5 months pregnant, you need to care for yourself and your baby. Is your partner supportive? What about your friends? Of course your mother is your priority at the moment, but I do not think she would happy with the notion that your priority is her rather than yourself and your baby.
It really is a miserable situation to be in. I can only try to empathise, so this comes with a massive cyberhug.
We are all siblings in grief.
Love, Christie xxx