Paul B3 said:
When you say its been potted , I would have thought a shrub/tree of that size would be struggling to intake enough water .With recent warm drying winds , your plant would have been unable to transpire at a pace to compensate . A second possible reason is Fireblight disease (I hope not) which affects members of the rose family ; symptoms include an apparent scorching of the leaves combined with leaf-curl ; exfoliation is then rapid and the plant normally dies .I lost a large specimen once ; it was growing in a moist position so drought wasn't responsible . I blame the above , (Fireblight) .
Well, that's something, at least her's are okay. I am stuck to be honest, as Paul says it may well be fireblight. Have a look at this info from the RHS https://www.rhs.org.uk/advice/profile?pid=160
I agree it would be better off in the ground than a pot. How long have you and your sister had them? Were her's planted in the ground straight away ?
Sister planted hers in the ground straight away,she's saying hers are fine actually
I would get a bigger pot and lightly feed it when needed, every 4-6 month.
But that original pic looks a lot sad, here's hoping and crossing fingers but hope is low, sorry.