Hello Rohima. They both should be fine to plant in the same spot if you add a little rootgrow (friendly root fungus) when you plant available at all good garden centres. One sachet £3.99 will be more than enough for two trees and you only do this once as the fungus stays on the roots for the trees life. It helps it with food uptake and keeps the roots healthy too.

Thank you fractal,that was very helpful. I would not have thought about using rootgrow. I was quite sad when i lost the plum tree as it was a mothers day present. I now a bit more of their needs so hopefully will be more successful 2nd time round. will wait until autumn tho.