Thanks for your question. As you pointed out, the yews do seem to mostly be thriving. There are two environmental factors to keep in mind. One, last summer's drought could have left the yews more susceptible to winter injury, which occurs when we have rapidly fluctuating temperatures (as we did last winter) and bright sunshine. Two, we had a wet spring, and the soil may not have been able to drain away excess water fast enough. Yews don't tolerate excessive moisture at their roots.

I would wait a few more weeks to see if the yellow/brown branches develop new growth. In the meantime, you can prune those dead branches and amend the soil around the base of the yews with some organic compost. Good luck!