Q.olive tree and 3 oleanders have gall
Olive tree covered with gall ‘nodes.’ Shrubs were trimmed back and are now covered with ‘nodes’ and very little leaves. Is there any cure?
You may need to dispose of the effected tree and plants if indeed they are infected with Crown Gall.
Here are links for you with more information.
https://www.gardeningknowhow.com/plant-problems/disease/how-to-fix-crown-gall.htm
https://www.gardeningknowhow.com/plant-problems/environmental/treating-leaf-gall-on-plants.htm
https://www.gardeningknowhow.com/edible/fruits/olive/olive-tree-care-information.htm
https://www.gardeningknowhow.com/ornamental/shrubs/oleander/oleander-growing-tips.htm