You should have time off over Christmas which is separate from your Half way weekend. can't remember how long the leave is, think it's just over a week. If your unlucky your weekend will fall at the same time as the Christmas break then they are combined lol
ATR is not an operational tour there's no need to keep people over Xmas. that will be worked out in the training programme. DS means "Directing Staff" ie your Cpls and Sgts etc, who certainly wont be spending Xmas training recruits.
However In phase two you may have a duty to do at some point over the holidays, same for proper units. I just spent Christmas in Northern Ireland for example, woopy f**in do.