So your DH has asked them to bring the presents over this Saturday, so you'll have them for Christmas morning as hoped? That's a fab outcome then!
I would have said to ask anyway, because I'm sure the grandparents would be happy to continue the Father Christmas belief at this stage in their lives too, especially as it's not the only gift they'll be giving.
I find out what DSs want from FC and then make sure that no one else buys it, so that it goes in their stocking (or under it, if it's too big) - they get that one main thing from FC, and then a few other little bits. Everything else they get comes from named people. This is also what my parents did and I continue it because I liked it that way. If ALL presents came from FC, it would feel weird and as though no one else in the family cared enough about them to give them presents, which doesn't work for me (although I'm sure other families manage it just fine).
My Dad and sister are in the UK and they like to see their presents being opened, so we either skype them while it's being done, or if that can't work, I film the children opening the presents and send them the film. Although I agree that presents should absolutely be about the person receiving them, it IS nice to see those presents being appreciated, and the look of wonder and joy on a child's face usually gives people a "warm fuzzy", so why deny them? But in the case of the OP, the grandparents are still going to get that with the other presents, so they're not missing out.
Glad it's resolved anyway, OP. :)