Absolutely ignore them! The estate is what was left when grandfather died - not everything he had in his possession several years ago!
This!
Otherwise you'll all be handing back the value of birthday presents etc.
And I'll bet he has given gifts t the others, too - it's just that they know about yours (how?), but you don't know about anything they were gifted.
The past is the past, a gift is a girl.
Surely, too, you'll have a share in the estate? Why will you have to give back 10 grand AND forgo your share? Or os the 10k + share what the gift came to? Because if it is that much, theremight (just might) be something to pay back.
However, I would have thought (NB I am NOT a lawyer) that you might have to pay tax on the value of the gift, but that would be the end of it - you would still be able to keep the gifted money, and be entitled to your share of the inheritance.
The GF wanted you two to have it - if he didn't, he wouldn't have given it to you.
(IME it's always the ones who never visited who make the most noise about getting their share)