Cherry Blossom tree issue

Hello, recently moved house and have a nice garden and now on a steep learning curve to keep it that way! My initial issue is a lovely cherry blossom tree in middle of lawn. It is just starting to blossom but noticed some smaller branches Have no blossom so probably dead? In particular one larger branch has some blossom on one of the small branches but the others nothing. I cut part of the smaller branch off and the wood was very soft, cutting further up still soft. Could it be diseased? I could cut the whole branch off near trunk to see if this is soft but this would drastically change shape of tree.

 

Without I picture I doubt you will get a positive answer.

 

Hear are some pictures, tried a close up as well

 

I'm trying to work out where the close ups are on the picture of the tree?