Looks like the rot on the left one may be spreading to the right one.
You should take them out of their pot and get rid of the rot.
Yes you may be able to take a cutting from the top of the rotten one. Just be certain that the cut edge is clean and white. No brown rot so keep cutting until you have a clean surface, then let it callus and start a new plant.
The rot may be in the soil so remove it and if the right hand plant looks healthy then pot it up with new well drained mix.
A photo of the base of the right hand plant after removing the soil might help us diagnose it. If any part of the trunk is mushy it should be cut away and allowed to heal.
