Thanks so much for reaching out and for providing pictures. The information that you've provided about the soil moisture and the pH is really helpful in terms of narrowing down what the potential issues could be with your yew. 

One possibility given the weather that we have is that the tips of the branches have been damaged by sun scald or heat stress. Even with deep watering, we have had unrelentingly hot days with intense sun, which can be a major stressor. New growth at the tips of branches or any areas that are newly pruned would be especially susceptible to this type of damage. If this is the cause, the yew should recover and you can prune off the brown pieces once the weather cools down a bit so that you don't risk further damage. Another thing to note is that yews like good drainage and are typically fairly drought resistant, so you want to be be careful not to overwater them. Overwatering can also lead to browning/yellowing. Both of these seem like the most likely causes of what may be happening to your yew. 

Keep an eye on them and see whether this browning continues to spread on the same yew or appears to be spreading to other yews. If so, please follow up and we can troubleshoot other possibilities for what may be going on.