Hi Gayatri and thanks for your pictures and question about your roses. I see two possibilities so I'll explain both and let you see which one matches best.

The first possibility is a tiny, tiny insect called thrips. I don't see signs of leaf deformity, but they can cause the buds to fail to open. If you see any signs like small black specks on leaves or pollen scattered on the leaves, you can try hosing the plants in the morning while you wait for the predatory insects to move in and control the population.
https://pnwhandbooks.org/insect/hort/landscape/common/landscape-thrips

The second possibility is Bullhead which happens when the flowers form in colder than normal weather. If this seems likely, you can cut off the heads that didn't open and the later ones should be fine.
https://pnwhandbooks.org/plantdisease/host-disease/rose-rosa-spp-hybrids-bullhead

Hopefully one of these will help your roses produce beautiful flowers again!