When you take on an animal you must accept full responsibility for them, which, reading between the lines, I'm sure you do. Even a younger, less mentally scarred dog, wouldn't understand suddenly being abandoned, could never know you would one day return. Your grandchildren can be told, whatever their ages, they'll see you again, & as others have said you can all FaceTime. Then the grandchildren can move on & enjoy their day. I have had to be completely alone for the last 2 Christmases & it sounds as if you will at least have company. Your dog might not have much longer - who knows. And cats, although they might not always show it, can be equally dependent. I would never trust anyone else to look after my 14yr old dog, despite her being a demanding little rescue who'd spent her first 12 yrs obviously being completely spoilt & who occasionally drives me to distraction. Christmas will come & go very quickly & then, hopefully, onwards & upwards.