Asking for advice: Dad has terminal cancer, need to spend summer with him - can a doctor's note help?

Assalamu alaikum, and thanks for reading. My dad has terminal lung cancer and doctors estimate he may have until about mid-August, though he seems to be getting worse day by day. He wants to be buried in our home country, and my mum has asked me to come after college finishes in June so I can spend what may be his last two months with him. I finish college in June, which would give me the chance to be with him. The problem is I work in retail and I’m not sure my manager will approve such a long leave. I’m wondering if getting a doctor’s note explaining my mental health and the stress of this situation would help. This is affecting me deeply and is making it hard to work. I don’t mind the leave being unpaid or losing paid holiday - my dad matters more than money. I’d ideally need around eight consecutive weeks because it’s so unpredictable how things will go. A few extra details: I’m over 18, I support my family somewhat (I do about 8 hours a week and sometimes overtime, I also buy groceries), and I have a small emergency savings cushion so short-term not working wouldn’t be impossible. My dad isn’t legally my dependent but he’s my father. I can’t realistically find another job right now - it took me a year to get this one and with the cost of living I can’t risk losing it. I’m in England, UK, so I know rules can vary. Has anyone had experience getting extended leave for this kind of family emergency? Would a doctor’s note about my mental health likely be enough, or should I say to my manager that this is a family emergency and ask directly? Any practical advice on talking to my employer, what paperwork I might need, or how to balance supporting my family while protecting my job would be so appreciated. JazakAllah khair for reading and for any help.