Holiday destination for the whole family?

[Dani]

So my dad's side of the family are all planning on going on holiday together the week after Christmas for a week. We need a destination though. It's going to be my grandad who is 76, 2 aunts, 2 uncles, my mum, my dad, my brother, my sister, 5 cousins and me. The "children" range will be aged 21-12 and the adults minus my grandad are around 40. It's only a week so long-haul flights wouldn't be very good. My grandad can do walking but would not do very active things whereas my cousins and I would. We either want somewhere very hot or very cold. Not interested in rain. So we are after somewhere not too far away with activities as well as possible sightseeing. Any ideas? Oh and we are in the UK.