First we would pay off our own mortgage, maybe buy some land and vuild our own house, so dh can have his techy bits as he wants. Then I would pay off existing mortgages in our families, both of them, every sibling, parents, grand parents and neices/nephews. We would not include cousins in this, neither of us are very close to them. If people don't have mortgage (e.g. parents) I would give them an equivalent sum. If people then choose to move, we would not help with a new house, unless they unexpectedly had triplets or the like.
I would do the same for close friends, depending on needs. If not, then perhaps a second car here, a holiday there, etc. Cousins would get the same.
Of course this would not need to be a significant win. I think most people have an average of about £150k outstanding so would need about a million for immediate family and ourselves, and a further million for friends and extended family. I enjoy my job so wouldn't want to retire, but would want to be comfortable, so prob £2.5-3 mil would do. (Are you listening, lottery fairy?)
Guess I should buy a ticket!