I had the very same situation years ago and I dug my heels in, at first I was flabbergasted at the words leaving his mouth then I came to the realisation that the core problem was jealousy.
So for the past 2 years you have worked together renovating properties, ok, that's good that you have worked together but now things have changed, you rightly so want to be a grandma and be part of your grandchild's life, what is wrong with that? Nothing is wrong with that, from what you have said it seems to point to throwing toys out of the pram and its extremely unfair to create this situation that you are now in.
I'm all for talking things through and working out a compromise but it seems despite you trying to do that, its to no avail, well wouldn't budge an inch, it's him who is being childish and jealous. Your relationship with your granddaughter is very precious and most certainly not up for negotiating anymore.