Sometimes we don’t always think alike or it can be a shock to your family when you start talking about end of life. Take your time talking and thinking together. Try to find out what is worrying them and explain why you want to talk about your advance care planning.
It might be helpful to discuss with your health and social care practitioner; as a sounding board, gain ideas how to talk to your family, or speak with your family on your behalf (with your permission).
If your family disagree you may like to have a look at a Lasting Power of Attorney (LPA) for health and care or an Advance Decision to Refuse Treatment (ADRT) as a way of addressing this.