fruit trees dying!

Hi All

I'm having a problem with my dwarf fruit trees I purchased a few months ago.

I bought them when they were already at full height but had no leaves so followed the instructions, planted them in some good multi purpose compost in a large enough container and put them on my patio.

My cherry tree was the first to start growing leaves and seemed to be doing well until about a month ago when all the leaves started turning brown and  dying back and the new shoots started turning brown...

Did a quick google and saw some advice that stated if the actual branches have gone brown inside then its dead/dying and to trim back to where its green again.

Did that and it hasn't stopped it, the whole thing is dead now

The rest of the trees (plum, apple, pear) started growing some good green leaves and looked fine but i noticed 2 days ago my apple tree on one of the branches the shoots have started to go brown now and seems to be going the same way as my cherry tree!

What can i do to save them?? They have plenty of sun and are watered regularly..

They have stones in the top of the pots which completely cover the compost, just to stop next doors cats using it as their toilet. could the stones be causing any problems?

Thanks in advance