Steve Thorn wrote:In general they should, and you probably won't have an issue. Sometimes certain varieties won't pollinate each other though, and if you know the names of the varieties that you have, you can check a pollination chart like this one that lists both varieties to be sure they will pollinate each other.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.burntridgenursery.com/text/Plumpollinationchart.pdf&ved=2ahUKEwjI-vzqrIHvAhVGMlkFHU_wBSkQFjAKegQIARAC&usg=AOvVaw1qCUsB0meHVO6vVRDIMnrR&cshid=1614129812776
You could also graft a different variety of plum onto one of the branches of your existing tree to get more pollination, if the two existing ones thst you have didn't pollinate each other.