Many thanks for your replies and taking the time to help me figure this out, I didn't realise the other information needed for this calculation. I have added the following:

UK based (population 60 million max)

Father died at 72 (heart disease)
Maternal Grandmother died at 85 (heart failure)

200 miles apart

Deaths within 12 hours of each other on same day in November

Only 2 surviving primary relatives - I thought having a brother sharing the probability meant that the probability is halved?

This happened to me. I have always believed I had more chance of winning the lottery (here in the UK that's a in 14 chance), but couldn't find a clear way of calculating the probability.

Thanks once again

CL