Posted: 07/04/2017 at 23:41
Depending on the variety, it could either be that they are deciduous types (the majority) which have been grown in artificial conditions and are now losing the older leaves now they are in the real world, or they are evergreen types which lose many of their leaves at this time of the year as they are replaced by new ones. Either way, the new growth looks healthy and there are clearly plenty of buds on the stems so I would say you have absolutely nothing to worry about.
However, I dfo think you are probably watering them too often and would cut down and only water them when the surface of the compost begins to dry out. Blueberries like damp but not waterlogged soil. Always use rainwater as tap water can be alkaline which they won't like at all.
I'm also assuming these are outside. They should not be grown indoors or under cover as they won't appreciate the dry air and heat; They are hardy outdoor plants and need a cold season to grow and fruit properly.