I would think you have a good chance of getting some seats on BA at T-355. We weren't able to make a booking for ourselves this year on the peak days (3/4 Jan, had to settle for MH) but had plenty of choice for my in-laws who come home from HKG on the 12th (booked last Jan). If you return in CW yes it will be 60k additional for the return rather than 90k. This would have to be added by phone (with mixed experience of having to pay the £15 offline fee).

Any partner bookings are still made through BA. Two legs with a stop can only be booked by phone, and there is no real benefit for which you would want to pay the offline fee. All BA and partner awards are cancelable for £30pp, done online unless something goes wrong (which usually brings a quicker refund than offline).