One tire went flat when a large bolt pierced the rubber. It is in the tread, but very near the sidewall. It is questionable whether the tire will be repairable. I won't have time to go to a tire shop for a few days, so I'm driving on the spare. If it cannot be repaired, it may be odd to have one brand new tire at this mileage. 27K miles is neither like new nor is it near worn out. Based on the condition of the tires, it seems like they could go to at least 50K miles before needing replacement. It may also be odd (handling/noise/vibration?) to have 2 new tires and two older tires. They are the standard 15" Yokohama Avids. If I buy 2 new tires, I might as well think about buying all new matching tires and upgrade to a quieter tire.
I had to replace a tire and repair a wheel after hitting some debris while driving on the freeway in my Camry SE. I changed just 2 tires, but I only had 5k miles on the other 2. It's been fine.
Your tires are probably below 7/32 I would wager. They should be replaced by 4/32 for safety reasons.I would replace at least two. Put the newer tires on the rear. The drawback to this idea is that you are likely to purchase the Energy Saver A/S based on your other questions in other threads. The $70 rebate is only good for the purchase of 4 tires.