I think that is very odd indeed.
Firstly missing you off - either it's from his parents, or it's not. If you are a couple, then, to me, that's very strange to just put it's from one of you.
Secondly, to put the name of someone who has passed away on a label is very strange, and would make me quite uncomfortable.
Thirdly, the idea of getting a "big" gift (or experience) "from deceased grandparent" - for just one of your 3 dc, is, again, very strange.
I would (have) ensured they all had some money put aside "from" the grandparent if that's what he wants to do with the inheritence - even the little one who wouldn't know at the moment, but will soon grow, and I'd like
to hope hear about the grandparent that loved them all equally.
Grieving or not, I couldn't allow my dh to do that to my dc