Help please, apple tree disease

Did you prune the tree thoroughly last winter , especially areas that may have shown signs of disease?
It’s possibly apple scab but people more knowledgable to me may confirm otherwise- pruning back infected areas will help prevent the spread,

How is the base of the tree? Is it kept clear of dead leaves and debris?

Sounds like either they were all purchased with the same disease or else, might be a soil issue - it was a very wet winter which could have added to things but with leaves falling off now as well on all 6, which are a range of varieties- that’s strange -for me it either points to a soil condition as the issue or that you purchased all 6 with that condition - maybe wait for someone else to appear here to provide their view but I’d go back to the center you purchased from with photos - don’t tell them you purchased there until after they give their view- they might just walk into admitting that they were a bad batch - but considering all 6 and different varieties it’s also possibly a soil issue

considering the early deterioration it does point towards apple scab- as opposed to brown rot which may be caused by wet winters and also birds damaging the fruit but it’s a bit too early for that - cut back infected areas and dispose of carefully - maybe consider a soil test or add chicken manure (readily available in garden shops) to see if it helps improve leave quality over summer

How to identify apple scab

Spots that are black or brown in colour develop on the leaves and fruits, from spring onwards. Affected leaves may fall early. On fruit, the spots may join up to form lesions which can split, allowing entry to other infections.
https://www.gardenersworld.com/how-to/grow-plants/apple-tree-diseases/