I think it's a wonderful idea to take your GC Xmas shopping, I'm sure they'd love it & why not! Maybe if you invite your D to join you, she'd be more up for it, perhaps she feels left out, or did the invite include her? How old are your GC?
Like Smileless I haven't seen my D & beloved GC for 5yrs. I had a very special bond with my GD & [I thought] D, as they lived with me before my GD's stepdad came along. I also loved my GS with all of my heart too. I was very good to them all as a family, but still got 'cut out'.
I sent my GC a letter from Father Xmas, they even complained about that. You had to put an age range for the C and as the GC were 18mnths & 30mnths I put 2yrs, which is right between the ages, but nasty s.i.l managed to turn this on it's head deeming the card was aimed at GD & not his son, he couldn't see it was between their ages exactly
I also asked my D if the GC would like to go and see Father Xmas at Altons garden centre, which is a really lovely place, you have to book and pay, not cheap, and I said we could all have a nice lunch after together, her included of course, she said she thought they were too young! For sure s.i.l in-put on the refusal. This was just before the big CO!
I wish you luck LindyLou xx