Your grape flower photos are not sufficiently in focus for me to see anything.

There are so many things that can go wrong with grapes, even when grown in the south of France. Cold weather during flowering can result in poor fruit set.

I'm growing a grape variety specially selected for British-like climates, Phoenix, and its fruit set fine, flowered quite some time ago now.

Of course blueberries need feeding, like most things. They also like it soggily damp, and, at least in many parts of Britain, it was very dry during flowering period.