
Do you suspect that the plants have shifted in the soil?
Can you pull the shrub to an upright position?
If they shrubs can be pulled into a more normal position, I would stake the plants.
Use protective clothing whenever working around Oleanders, as all parts of plant are poisonous.
Here are some links with more information.
https://www.gardeningknowhow.com/ornamental/trees/tgen/straighten-tree.htm
https://www.gardeningknowhow.com/ornamental/shrubs/oleander/oleander-growing-tips.htm
https://www.gardeningknowhow.com/ornamental/shrubs/oleander/pruning-oleander-shrubs.htm