Since you said SIX plants, I'm assuming yours are planted in the ground. The photo seems to show that the grass is growing right up against this plant?
If so, blueberries are shallow-rooted and don't take well to competition. Your plants may be stressed. Also, as Jona said blueberries need acidic soil and, where grass is growing well, the pH of the soil is probably higher than what they need. I would check the pH and apply amendment like sulfur or gypsum, water in well and lay 4~5 sheet layer of newspaper, then mulch with acidic mulch like shredded composted pine bark or pine needles mixed with compost.
Keep in mind too if the weather is getting cold where you are, that blueberries are deciduous. The leaves on two of my blueberries in the front yard got hit by the frost and turned beautiful red. The ones in the back yard are more protected so the leaves just got splotchy and fell off -- not much of a color show.