Help its dying!!!!!

Ok so Im an absolute beginner, dont use any gardening jargon or I will be lost. I bought an older property with a mature garden and last year the 3 victoria plum trees were loaded with fruit. However this year one of the three has died completely, the second has a silvery colour to the leaves and has only 1 small plum and the a number of the branches appear dead and have no leaves, some of the leaves have multiple small holes with brown rings around them. The third tree appears healthy but has only 4 pieces of fruit however is being badly sheltered by an out of control hedge and alder trees.

what can i do for tree no. 2 and do i need to just cut the hedge away from around tree no.3????

Please any help would be much appreciatedd

 

Hey Shiney thanks for the info, Ive been out of the country with so hopefully will get opportunity in morning to do something with the tree

 

Thanks for your help shiney