plum tree identification

I am new to this site, I think I shuld have used this avenue for my question, I have uploaded photo's of these plum trees, they are not producing and are going on 6 years old, i can not remember the name of them, I have 2, I do not know whether they are self polinating or not, due to not knowing the tree type. Thanks

 

It looks like a Japanese type plum, usually they do require a pollinator to do their best.