The decisions have to be binary or else 34% of voters could decide for the remaining 66% - how would this go down ? I think you know !
So, it has to be a series of binary decisions and everyone has to vote on each of them
1 Leave or Remain
2 If leave, Deal or No Deal
3 If Deal, Mrs May's deal or WTO
Thus the issue would be decided at stage 1 if Remain gets >50% but goes to stage 2 if Leave gets >50%
At stage 2, with everyone voting, the issue is decided if No Deal wins, else goes to stage 3
At stage 3, with everyone voting, either accept Mrs May's deal or WTO terms.
If everyone follows the rules, you will emerge with something that >50% of the voters voted for.
Too complicated ?