Medlar

Hello, I have a small Medlar tree which I would like to prune. I can't tell whether the tree (?) or shrub growing very closely to it - or through it - is where it has been grafted onto a rootstock or whether the other tree is separate. I am not sure what the secondary plant is but it seems to be taking over.... I don't want to kill either but they are now overshadowing an area I'd like to open up as it gets very dry. Any thoughts or advice? Thank you.