Welcome to COL, sounds like a very busy household you have there!
There is just myself and OH at ours, plus Duggie, who is almost 7 months, and Tia, a rescue, who is 4 and a half, they are both black show Cockers. I also have 3 rescue rats and 1 rescued hamster - kept well away from the dogs! Duggie loves them and used to play with them under supervision, but I wouldn't let Tia even see them, as she has been known to catch rabbits in her last home, and recently brought us a lovely gift of a pigeon.
I think what Jo meant about your breeder's motives, is that no responsible breeder or rescue would ever rehome a dog at Christmas time, as there are just far too many who end up unwanted and kicked out. It is also a very busy time to bring a new dog into the home, and can be very frightening for them. It seems you are willing to learn all you can and to give your pup a great home, but who knows what may happen to the rest of the litter.
Jo and I are both involved in rescue, and have seen it numerous times, unfortunately.
Would it be possible for the breeder to hold on to Daisy for you until the hecticness of Christmas is over, then she could be introduced to the family when everything is more settled, and nice and quiet? Your Christmas day will be spent taking your new pup out to the garden every half hour, plus she will want to sleep a lot and may get upset if the children are overexcited and trying to play with her.